Before you drop an extra 150 to 200 to jump from an i5 to an i7, ask yourself this... Do you need hyperthreading?
Is this strictly a gaming rig, or is it gonna be tasked with heavy Photoshop and video editing tasks?
Gaming rig only... i5 Hyperthreading just isn't an important feature for games.
Then just to be sure... benchmark it...
http://www.anandtech.com/bench/CPU/2 And when you look at the results, remember that if chip A (at $300) gets 200 fps and chip B (at $175) gets 197 FPS (I made all those numbers up... obviously, to illustrate a point) and a movie is 24 FPS and video in 30 fps and Crysis looks awesome at 60 fps then chip B is better than chip A from a cost/benefit perspective. Save some money that can buy more ram or some games or a bag of weed or dinner for you and hot gamer chick (or guy, depending on whatever)
...and fps isn't really that big of deal, unless you just wanna shell out cash for bragging rights.
No industry is more full of hype and myths than PC hardware. When someone is raving about specs and stats they are usually raving about attributes they can measure but not see. Don't get too wrapped up in having the latest and greatest.
Besides, the obsolescence path ain't what it used to be. Your next machine will surely be an effective machine for longer than your last one.