Intel Core i3 530 Review: Great for Overclockers & Gamers
 

Priced at $113 (and selling for about $125 on the street) the 530 runs at 2.93GHz and features no turbo modes. It’ll run at 1.33GHz at its lowest frequency, and no faster than 2.93GHz at full load. The missing turbo boost is almost all you sacrifice as the 530 still has a hefty 4MB L3 cache shared between both cores. Each core gets a 256KB 10-cycle L2, just like the i5s and i7s.

The un-core is clocked at 2.13GHz, down from 2.40GHz in the i5. That should hurt performance a bit compared to our simulated i3 in the launch article. Aside from Turbo the other thing you give up with the i3 is AES acceleration. Westmere's AES New Instructions (AES-NI) are disabled on all of the i3s in typical Intel fashion. There has to be some reason for users to opt for a Core i5 instead.

http://www.anandtech.com/cpuchipsets...oc.aspx?i=3724

No need to upgrade to Core i3/i5 with IGP if you currently have Core 2 Duo Wolfdale with dedicated GFX
http://www.anandtech.com/bench/default.aspx?p=56&p2=118

clock for clock Core i3/i5 is not noticeably faster in my humble opinion

And if you've got a Conroe @ 3.4 - also no reason to upgrade? :)

your upgrade path should be S1366 Core i7 in my humble opinion to get a noticeable speed boost
going either Core i5 clarkdale or AMD Phenom won't make a huge amount of difference;

S1156 I would not invest in for the price/performance sake; seeing as the S1366 platform is more mature and geared towards better performance