i will overclock the cpu, but idk which cpu to buy, i will use it mostly for gaming, the 2500k or 3570k? i will be water cooling it, i will oc it up as far as it goes, please someone tell me which will be better?
Getting a 2500k over a 3570k (if prices are similar) makes no sense if you are water cooling. With water cooling, you are already handling the higher heat issue of the i5 3570k, thus making it ideal to get a 3570k as it is already ~10% faster than a 2500k. Plus, there is not a 1 for 1 relationship with overclocking. For example, a 10% overclock does not necessarily yield an exact 10% increase in performance. So, you will have to overclock that 2500k between 10% - 15% to get comparable performance to the 3570k at stock speeds. I have a 3570k and on the stock cooler can run it oc'd to 4 ghz and never hit above 72 Celsius on my hottest core and am usually in the 60s while gaming.
In other words, the heat will not be a major factor for either chip if you are water cooling, so why waste some of the performance potential by getting a 2500k that will right out of the gate need a 10% to 15% oc just to match the 3570k, especially when the 3570k can oc up to ~5 ghz with proper cooling.
Also, don't overlook getting a good motherboard that is friendly to overclocking. An ASUS Z-77 V Pro or above should get the job done without breaking the bank. For example, you can pick up a 3570k for about $189 + tax at MicroCenter if you live near one. They also give $50 off for a motherboard if bought in combo.
I should add that the 2500k is a great chip and can oc to just as high as the 3570k. Some even say it is more consistent in reaching 5 ghz than the 3570k, but imo I would never push my chips to the max for the very marginal increase in performance going from say 4.7 or 4.8 ghz to 5 ghz.
Also, and this is VERY important if you plan to invest heavily in future gpus. The 2500k can only do PCI express 2.0 and will NOT do 3.0 even if your mobo can do it. The 3570k does PCI express 3.0. Not a major issue for most people at the moment as PCI express 2.0 still has enough bandwidth, but with the second round of PCI express 3.0 cards coming out in the next several months, 2.0 will be showing its age soon enough.
Once you break it down, the advantages of the 3570k are fairly subtle but significant, and your average joe consumer with a little tech knowledge doesn't usually factor in what I've just pointed out to you in these two posts.