The cheapest overclockable Sandy Bridge is the 2500K. The i5 2300 and up have Turbo Boost though.http://www.newegg.com/Product/ProductList.aspx?Submit=ENE&N=100007671%20600095610&IsNodeId=1&name=LGA%201155
If you are gaming forget AMD. The i3 2100 beats the 1055T Thuban in all gaming benchmarks ( dual core beating a hexacore).http://www.anandtech.com/bench/Product/147?vs=289
I disagree.The phenom 2 1055t has a very low clock speed and games aren't optimised to take advantage of its extra cores efficiently.Even so,getting the 1055t to 4ghz will reduce the bottleneck and destroy the i3.Furthermore the x6 also beats the i3 at every heavily multithreaded application.Then there is the matter of high resolutions which minimise the bottleneck and the fact that the i3 can't be overlocked to increase its performance.
i3 vs phenom 2 x6 is a win for the AMD side.Still,I can't deny that the i5 2500k is a much better performer than the phenom 2 x6.Even my "old" i5 750 beats it in some cases(gaming mostly).