The main purpose of the system is gaming and playing multi-media files on a flatscreen TV. I had originally picked a K series chip because I know they are much more friendly to overclocking. I have never overclocked before and was going to start researching it, but before I do I want to know, will it really impact gaming or playing movies?
If it will only have a slight improvement, or no improvement at all, then I think I'd be better off getting a less expensive chip and an H77 Ivy Bridge mobo to afford an SSD on my budget.
Second question, if I overclock that chip to the 4.2-4.4 GHz range I see most people doing, do I need an aftermarket cooler?
For any overclocking past 'turbo' setting an aftermarket cooler is highly recommended. Will overclocking help gaming? Oh yeah, depending upon the game, the difference can be remarkable, up to 50% frame rate improvement in CPU intensive games (FSX, Starcraft 2, WoW, CIV 5, BF 3, GTA 4, etc.) with an aggressive overclock, 15%-20% improvement over stock might be a realistic expectation. Doesn't seem to have much, if any, impact on watching vids and less CPU intensive activities.
Hope it covers your questions
2600k 3.4Ghz stock
16GB of 1600mhz ram
Now, stock it's a pretty decent machine and will run any game on the market. The GPU's might not handle every game at max but they do hold their own. The CPU is pretty much not a problem with most games as it's still close to the top of the performance tier in gaming.
Now two examples for you...
Battlefield 3 is a graphics cards "general" benchmark these days. At stock I can run pretty decent settings (minus anti aliasing but that's the GPU's memory fault). Stock is at 910Mhz. Now when I do run fraps; I would get 45-50FPS averages during gameplay. This was decent but once I clocked the pair of them to 1Ghz and boosted the shader; the machine pulled 55-60fps. (Remember, scaling doesn't effect a single card so 2 cards at 90mhz overclock is going to be a big gain compared to a single card at 90mhz). Now as for the CPU at stock clock 3.4Ghz to 4.4Ghz.. There's almost zero gain in framerate and/or performance of the game.
Now a game like Planetside 2.. Overclocking the GPU's I have had little effect on the game; maybe 5FPS total. However, from 3.4Ghz to 4.4Ghz there is a GIANT gain in FPS which was probably around 20fps or so, maybe more.
The biggest thing I'm getting at here is it depends on the software. Plantside 2 is heavily CPU dependent. Even if you have a just monstrosity for a GPU; a bad CPU is going to hold that game back whereas Battlefield 3 may run perfect. Having a bad GPU and an awesome CPU might make Planetside 2 run awesome while Battlefield 3's performance would be down the crapper.
So take those things into account. Each game is different; so don't expect every game to get good FPS gains because of overclocking the GPU and/or CPU. However, don't expect some games not to truly become awesome with overclocks. As a matter of fact Metro2333 ran so much better on my machine with the GPU's and the CPU overclocked. It was almost like I dropped a better GPU in the thing!