U wont get equivalent performance as E6750 with any current X2 proccy. But try Phenom 9500 which is for 8k range. Its a quad.
And Gigabyte 780G mobo @ 4.6~4.8k is a very gud deal. It has DX 10 IGP nd performs better than 8400GS, PCIE 2.0 , DDR2 1066 dual channel support and is spider platform and supports AM2+ proccys nd older AM2 also.
I think Phenom 9500 @ 7.8~8k is better than E6750 @ 7k.
http://www.cpubenchmark.net/high_end_cpus.html
But E8400 oced wud be real gud. It can take 4Ghz easily on stock cooling provided u have gud memory modules and a cool ocing mobo.
For Intel, get E8400 and Abit IP35-E for 8k and 4.6k. But that mobo dun have IGP, SO need to get atleast 8400GS for 2.2k.