My brother got an i5 3750k over the summer, and he's been able to play almost all his Wii games at 60fps, withstanding emulator issues in general. That's without an overclock mind you. Getting a nice graphics card will allow you to run higher native resolutions without a performance hit either; but you can also skimp and run games at a lower maximum resolution and save a performance hit and get a lower tier graphics card too.
If you're going to be serious about wanting to build a desktop, now or in the future, let us know and we'll help you out as best we can. Next to that, always consult sites like reddit for awesome savings:
http://www.reddit.com/r/buildapcsales
Besides good finds, a little bit of searching can shave off $100-$200 depending on your tastes and what you want or would be using the computer for. This usually involves recognizing that you can get a mobo with less features, because you're probably not going to use the three different graphics card slots or won't ever be using more than 16GB RAM (4GB is still modestly adequate for gaming!) or need 6 HDD running at the same time. All you'd really want to look for is reliability, and next to that, overclock potential.
I got the same processor as my bro a couple months back, and I was playing FFXII two days ago at 60fps with 3x native resolution (over 1920x1080). An i7 is overkill for almost anything asides from rendering/algorithmic stuff. Emulators would benefit, but the pricetag--unless you live near a microcenter or whatever that other store is--isn't worth it (sometimes they drop to the same price as an i5).
But yeah. Personally, I have SpeedFan running to note my temps, but CPUID is nicer as it will keep a tally of your lowest, current, and highest temps as long as it's been running. It's a nice reference, but SpeedFan also can graph temps visually if you like to see/need to compare stress points during performance.