I have an intel quad core Q8300 @2.5GHz and I wanna upgrade for many reasons.
1. It gets TOO hot, right now it's idling at 59C.
2. I'm planning on buying TERA and Guild Wars 2 and I think My CPU is bottlenecking my Radeon HD 6850.
3. I think overall this CPU heats up the whole computer, my GPU sometimes idles over 45C
4. I currently have a motherboard which doesn't allow me to overclock my cpu
5. many other reasons.
So my question is if I buy an intel i5 2500k will I get a better framerate for mmos, fps, etc?
I have a pretty old motherboard, an Intel G43 Express so I guess I have to upgrade my motherboard too, which would be the cheapest one to support sandy bridge?
Your CPU doesn't tend to dictate the fps you get in games...that's your GPU's job, generally. If you get an i5-2500K you'll have a newer system that'll last longer, it'll run cooler and you can overclock.
Ivybridge should be out reasonably soon; I would imagine 2-3 months before the parts are on the market and readily available (including early-rush buyers). However, that's conjecture...it may be sooner or later.
As for mobos, if you're get an i5-2500K then it's really set for overclocking...so you need a P67 or Z68 motherboard. The ones sitting around the £130 mark (about $180 I think) tend to be good as they have a wide range of overclocking features without breaking the bank.
The new AMD 7xxx and Nvidia 6xx series GPUs are heat-efficient due to the 28nm process used to make them...you've not said what GPU you have right now so I can't really comment further.
If you have time to wait, I'd say hold off...with the new GPUs and CPUs coming out rather soon, there's not much point in upgrading just yet.