Although no one can truly give you an answer to that, we sure as heck can guesstimate!
Most hardware will be up to par, if it's top of the line (as yours is) for 4 years. The HD 5950 was released over 4 years ago, I believe 5 perhaps, and it's still packing a medium-ish punch in today's gaming.
Having two of the cards would keep you up for a while longer, given your titles support crossfire.
Don't take my, or anyone's, word for it though. With increasing optimization, and speedy development, you never know!