I have an i5 and an i7. They are both Lynnfields at 2.8 GHZ. They both boot at exactly the same time. Unless you have a specific application that can take advantage of the i7's Hyperthreading I would save the money and go with the i5.
i overclocked my intel i5,750 to 3,6ghz. 200 multiply 18, and run at 38 degree idle, so thats very good, i have a msi mainbord, and 8gb ram. big cooler, hehe. ram frekvence 1200, at 1,30 volt. Modell P55A-G55(MS-7668). 8.GB Dubbel-Kanal DDR3 @ 598MHz (6-6-6-15) i5 is good as i7, just overclock alittle. i5 and i7 are made for do overclocking, and you save at least 130 usd.
Generally speaking, it is better to buy an i5 vs an i7 because of the lack of programs that take advantage of HyperTheading.
For me, the only program that I use which takes advantage of HT is encoding videos using x.264 in Handbrake. I think the benchmarks I've looked at a while ago showed that an i7 was about 25% faster at video encoding than an i5 of the clock same speed.
Therefore, I need to determine if this 25% performance increase for Handbrake is worth the extra $75 - $100 for an i7 CPU over an i5 CPU.
Games do not benefit, and I actually recall a minor performance penalty with an i7 vs. an i5 of the same clock speed.