Which 6950 is it? ( some are clocked higher then others) The 1055T comes at 2.8 ghz so It would bottle neck pretty fast I would think with the high end GPUs. I personally run a 6850 with one and its fine. Are you willing to overclock at all? Many can PC a 1055T to 3.5-3.8(sometimes 4.0) and get HUGE gains.
Why are you asking this question? Are you buying a 6950 or buying a 1055T or both? we could suggest better alternatives for your needs if you have more information on what you want.
I am selling a computer that has both. The 6950 is an XFX reference version. I had a liquid cooler on the CPU and had it overclocked to 3.2 with absolutely no issues. However, the person I am selling to is nervous about having liquid inside his computer so I am putting in a low profile air cooler I have laying around instead. With the lower performance cooling I do not want to OC. I guess I'll just give it a try and watch the temps and see.
Just one 6950 should not bottleneck. If the 3.2 had no issues it should be fine. the 1055T has a turbo option that turns the first couple cores to 3.2 by default even with 2.8 ghz as the default. Should be no problem.