GTX 550ti 2gb here....I use the current release (285.62).
There are no drivers out there, beta, old or current release that will improve performance for this game....as of right now, it's just a buggy, poorly coded engine, which hopefully will be patched.
I suggest using current drivers.
To the post above regarding DirectX 9.....you shouldnt have to do that.....even if you have a DirectX 11 card....Windows Updates and drivers for graphics cards already provide DX9 drivers. No need.