I really dont know what to get here. I'm doing this build as a home/office work computer and I've been going back and forth between the I3 and I5 2500. The I3 is dual core with hyper threading while the I5 has four actual cores but no hyperthreading. I guess what I'm afraid of is the I3 will underperform because the dual core will bottleneck. But how much better will the I5 be with four actual cores but no hyperthreading?
If you're doing the basics of web browsing, office documents and videos then the i3 is more than enough. The only reason you'd really want the i5 over the i3 is if you were going to play games at high settings.
Yeah, for simple office tasks the i3 will be more than enough.
While a program like Excel can make use of a quad core CPU, there will be no noticeable performance increase unless you are doing some complex financial or scientific modelling. If that's the case, then I recommend waiting for Ivy Bridge since those two tasks uses AVX instruction sets and IB's upgraded AVX instruction set is estimated to give up to a 30% increase in performance for financial and scientific modelling.
The updated AVX instruction set applies to all Ivy Bridge CPUs. Just be aware that AVX (Advanced Vector Extensions) have very limited and specific uses. If you're not doing financial or scientific calculations that takes advantage of the updated AVX instruction set, then you will not see much improvement over Sandy Bridge CPUs other than the difference in clockspeed and the potential increase in Ivy Bridge's IPC (instruction per cycle).
I agree with jaguarskx. For Microsoft Office, CPU really doesn't matter unless you are doing heavy Excel or Access work. I do a lot with Word 2007 (working with 300+ page files at least an hour a day), and I can't tell the difference between a brand new i5-2500K (some times work at my buddy's house who's a gamer), and my old Pentium E2200 desktop and my old Core2Duo laptop.
My thought is if this is an office machine, I personally would go with an AMD Llano. That way, I know I got a decent video card for light gaming and such.