It has been months since the official release of CUDA 6.5 and it is about time to upgrade from 5.0. The performance improvements in double precision is noticeable in the new release, and there is no change of code required. The toolkit download is around 1GB and the installation is flawless (except DOSBos crashed in the middle).
Looking forward to CUDA 7.0. As of writing it is in Release Candidate status.