Not quite on the same level. My 965 @ 4,336 Mhz was within a few percent of a stock 2500k. In some situations the 965 would be faster, in others the 2500k would be.
Also, keep in mind that most 2500k can easily reach the upper 4Ghz range.
Here is a comparison of my 7870XT with a stock 2500k and a 965 @ 4.336Mhz. Keep in mind the 7870XT was overclocked 100Mhz faster on the 2500k.
Stock 2500k - score 5890 - http://www.3dmark.com/fs/265481
7870XT @ 1200Mhz core / 1600Mhz memory
965 @ 4.336 - score 5535 - http://www.3dmark.com/fs/225687
7870XT @ 1100Mhz core / 1600Mhz memory
With the 7870XT being clocked the same as the 2500k, I would guess the score would be about 100 - 200 higher.
Also, notice the 965's physics score compared to the 2500k.
Yeah, that makes me want to just save up for a 2500k/3570k, new mobo, and 1.5v RAM and overclock that CPU to see what insane performance advantage I'd get over my barely OC'd 965 BE. Odd that the 965 still has an advantage in the physics benchmark, do you think at stock 3.4ghz it would still have that advantage?
It's been a while but I think a stock 965 scores somewhere around 5000 in the Firestrike CPU tests.
Here is a straight on comparison of the 2500K and the 965 @ 4,336Mhz.
Same 7870XT running at the same clock speeds.
965 @ 4,336Mhz -score 5873 -http://www.3dmark.com/fs/293460
2500k @ stock - score 5890 - http://www.3dmark.com/fs/265481
So 17 points difference. I would call that within the margin of error for 3dmark but the score is still higher with the stock 2500k.
Here are an FX6300 and 8350 also with same 7870XT at 1200Mhz core / 1600 Mhz memory, just for comparison...
FX6300 @ 4,739Mhz - score 5964 - http://www.3dmark.com/fs/323105
FX8350 @ 4,628Mhz - score 6122 - http://www.3dmark.com/fs/343074
However, the CPU tests tell a different story..
965 @ 4,336 - score 6373
2500k @ stock -score 6200
6350 @ 4,739 - score 7375
8350 @ 4,268 - score 8923
You don't mention what your GPU is or what motherboard you have.
I would suggest sticking with an AMD CPU if your motherboard will support the newer FX processors and dumping the remainder on a better or second video card. If however, your board will not support the newer FX CPUs, then I would seriously consider a 3570K with a good motherboard.