NVIDIA CUDA DRIVER 340.46

NVidia Cuda Driver 340.46 is available from NVidia as part of the CUDA 6.5 package. It contains PhysX, the 3D Vision Driver, the HD Audio Driver, and NVidia Update. You don't need a modified inf file to install it, and don't need to boot up Win 8.1 in Disable Driver Signature mode to install it. It is from the same driver family as driver 340.51 and 340.43.
 
Link to driver on NVidia site: https://developer.nvidia.com/rdp/cuda-65-rc-toolkit-download
You will need to create an account if you don't have one already.

Driver 340.51 is r340_00-143, DriverVer = 07/02/2014, 9.18.13.4051
Driver 340.46 is r340_00-128, DriverVer = 06/22/2014, 9.18.13.4046
Driver 340.43 is r340_00-116, DriverVer = 06/12/2014, 9.18.13.4043
Driver 337.91 is r337_41-10, DriverVer = 05/21/2014, 9.18.13.3791
Driver 337.90 is r337_00-191, DriverVer = 05/20/2014, 9.18.13.3790
Driver 337.88 is r337_00-189, DriverVer = 05/19/2014, 9.18.13.3788