What are the rest your system specs? (CPU,Mobo,RAM,etc.)
That Corsair 430watt is actually only capable of 333 watts on the 12/v rail.The average total system draw with a 6950 1G is about 326 watts.
We need to know your budget for the PSU and what your system specs are before we can give a good suggestion.The PSU is one of the most important parts of the PC so don't cheap out on it because if it fails it can take other compoents with it,such as your 6950.
You could go with a 500watt and still be ok for a single 6950 but it's always good to get more than you need.Thinking ahead is always good.You could bring the PSU your buying now with you onto another build.Graphics will always get more demanding which will make any current GPU get old very fast.Power is always the same.