Do i need to overclock a 2500k?

No, even at stock the 2500k beats even a fx-8150 in games, so you should be fine there.

Overclocking gives you more performance for the same money, and yes it may increase your frame rate, depending on the game (if cpu or gpu oriented).

You will want a good video card for games though. Do you have any in mind or know which ones are in the builds?

At stock speed a Core i5-2500k can outperform an overclocked Phenom II X4 or Bulldozer CPU. You do not need to overclock the i5-2500k if you don't want to.

Most games are limited by the GPU not the CPU. A faster CPU can improve frame rates by a few extra frames, but performance increase will not be as dramatic as installing a faster video card.

The 2 builds are as follows.
AMD:
case - http://www.newegg.com/Product/Product.aspx?Item=N82E168...
mobo - http://www.newegg.com/Product/Product.aspx?Item=N82E168...
video - http://www.newegg.com/Product/Product.aspx?Item=N82E168...
power - http://www.newegg.com/Product/Product.aspx?Item=N82E168...
cpu - fx-6100 3.3ghz 6-core
RAM - http://www.newegg.com/Product/Product.aspx?Item=N82E168...
HDD - WB caviar 2tb 7200 rpm

Intel
i5 2500k cpu
same case
MOBO - i am having trouble choosing a good intel board, but im thinking http://www.newegg.com/Product/Product.aspx?Item=N82E168...
same video card
same power
same ram
same hdd
* any help with a better build is always welcome, im wanting to game mostly, play BF3, mwf3, basically all the high end games at the highest possible settings while also recording using fraps or something

The 2500k is very good and overclocking is very easy, make sure to get an after market heatsink like a cooler master hyper 212 which will give you very very good temps during overclocking. This would be a board I would recommend: http://www.newegg.com/Product/Product.aspx?Item=N82E168...

every one says that overclocking the 2500k is very easy, from the videos ive seen and what ive read it seems sort of complicated

All you have to do is go into bios and change the multiplier from 33 to 45(multiples of 100mhz) disable intel turbo boost and intel speed step and bam you have a 4.5ghz i5-2500k!

I dont have to do anything with voltages or anything else? cause if thats all there is to it, then yea id prolly oc, i just thought it was more complicated

I'm not even sure you need to disable speedstep etc. if you back it down to 44 (4.4)
No voltages are common at that kind of level, to go higher you need voltage, but do you really need to go higher?

You're not going to hit 4.5 at stock voltage, not even on a golden chip, but finding the right voltage for your chip and board is a quick process, even for a beginner.

Yes if you get a 2500k you need to OC it, if you don't you suck. Plenty of dudes here will help you with questions, just get a half decent cooler and go for it.

OCing can harm your PC right? D:

I never OCed before...

Depends, if you go too far with voltages, or not far enough with cooling, then yes it can, but with no voltage increase and appropriate cooling there is not that much risk if it is stable.

The ´K´ in the i5 2500K means it has potential for overclock. If you are not confortable overclocking it, then you should take a cpu without the ´K´.

Both i5 2500K and i5 2500 are similar cpus, apart from its OC ability http://ark.intel.com/compare/52210,52209

So, if you decide not to overclock, then get an i5 2500 (without `K ´).

So its all about cooling?

May i ask what temperature can my pc take?

~i7-2600k
~Xion HP-1216B Five Heatpipes Direct Core Contact Copper Heatsink CPU Cooling Fan
~ASUS P8Z68-V PRO
~8GB Corsair Memory
~1000w Power Supply
~AMD Radeon HD 6970
~Zalman z9+ Case = 7 fans + standard coolant
I know i don't need to OC but meh curious D:

Difficult to say, but the CPU case temp is 72C, so if you are observant you'll have plenty of time to spot issues.

Oc to 4ghz and you will see a great increase in performance.

Some proof is in order, it is game dependent. BF3 no difference in overclocking. http://www.tomshardware.com/reviews/battlefield-3-graph... Skyrim has a 10 fps increase from 3ghz to 4ghz. http://www.tomshardware.com/reviews/skyrim-performance-...

No need to turn off speedstep unless you're extreme overclocking 5ghz+. And I would not recommend auto volting. For lowest vcore OC, set vcore offset to -.05 and set the multiplier as high until it is unstable probably around 40. I've got the 212+ which is $25 at 4.6ghz, gaming never goes above 60C (stock cm paste). Intel rates the tcase at 72C as monkey said. Google is getting $40 for that xion, a bad deal imo. What is your budget?

May i ask how many FPS i can get with the list i pasted here without OCing.. with BF3

Tom's doesn't overclock when benchmarking games not to mention I said OC doesn't affect BF3. From the same article: http://www.tomshardware.com/reviews/battlefield-3-graph...  

what screen size, have a look at tom BF3 article, since its CPU indepented and your card was used you'll get a good idea.

BF3 is virtually unaffected by CPU power. It's GPU intensive.

he also posted a gpu.

Overclock your gpu  

he says i wont get 4.5ghz at stock voltage, so what voltage should i set it to? how do i find the right voltage?

4.5ghz is usually around 1.3v. You need to test stability at whatever voltage and multiplier you set. If it's stable then you can either lower the volts or raise the multiplier until it's unstable.

There's a lot of guides about OC your CPU on the internet. You shouldn't OC your CPU if you don't have a good cooler. Good cooler will keep your CPU temp down while it's OCed and run at full load. You should do a lot of readings first to know what you'll get into. Anyway, it's pointless to extreme OC your CPU because you won't be needing all that power. The most important thing is to keep your CPU temp within safe area. That's depend on temperature where you live, type of cooler, thermal compound... I say you keep your CPU at stock voltage, raise your multipliers to 40x, then test with Prime95 with Realtemp or HWMonitor for temp monitor. If you get no bluescreen or freeze then you can raise you multipliers 1 by 1. Test it each time until you get bluescreen or freeze or your system won't be able to boot. Then lower your multiplier by 1. You can keep everything else on default. That's your CPU max at default voltage. If you decide to clock higher, then you have to raise your vcore voltage. Most of MB nowadays have a feature called DVID => Dynamic Vcore that you can add more voltage to your CPU to keep it stable. Remember to keep your eyes on the temp. I suggest you don't go over 80C. For a beginner, you need to read a lot first before you do extreme clocking.

My i5-2500k @4.4GHz stable on stock voltage. FYI I did successfully OC it to 5GHz stable but I'd rather have the speed it has now with 65C at full load by P95 and idle around 30C. I'm happy with mine @4.4GHz. I hope you too will find your goal in OCing your CPU.

Oh! To answer your question: No, you don't "need" to OC your i5k. But it's such a waste if you don't.