Only matters for single-threaded programs
I opted for the i7 over the i5 (2011 13") because of Solidworks. I don't know about the other cad programs, but the bottleneck for SW is cpu speed. The i7 (supposedly) has turbo taking it from 2.7 to 3.2(IIRC). That means it will be ~17% faster (no turbo) or ~39% faster (if turbo exists) for those single threaded bottleneck programs.
But if you aren't using something that requires high clock speeds, get the i5.
I opted for the i7 over the i5 (2011 13") because of Solidworks. I don't know about the other cad programs, but the bottleneck for SW is cpu speed. The i7 (supposedly) has turbo taking it from 2.7 to 3.2(IIRC). That means it will be ~17% faster (no turbo) or ~39% faster (if turbo exists) for those single threaded bottleneck programs.
But if you aren't using something that requires high clock speeds, get the i5.