These boxes aren't called troll boxes for no reason!

CUDA 6.0 RC is available. You have to be a registered developer though
https://developer.nvidia.com/user

compile cudaminer and compare results. the T kernel for keccak might be interesting to check out.
In CUDA 5.5 it gives a rather shocking performance.

Christian

Unified Memory -- Simplifies programming by enabling applications to access CPU and GPU memory without the need to manually copy data from one to the other, and makes it easier to add support for GPU acceleration in a wide range of programming languages.