GPU Performance Advice wanted for Lightroom CC

Currently running a Nvidia Quadro K1200 with a HP 5K monitor and a ViewSonic 1080 monitor. I do know how to monitor CPU and I/O performance, identifying and resolving bottlenecks, however I've not found a tool for monitoring the video card. I won't go into all the reasons that this could be tricky as I'm not there yet. I've also witnessed unannounced Lightroom GPU related performance improvements for specific brand RAW files, the latest about a month ago for the Fuji X-T1 RAW files. Had no impact on the Nikon D300S files. Some of the adjustment brushes improved by about 4X for the Fuji files.

So I'm trying to find out which factors significantly impact GPU benefits in Lightroom to determine whether I should upgrade. I'm not looking for a 20% improvement but rather 2-4X. These are the cards I'm considering with the K1200 included as a baseline:

       ------ memory -----   CUDA

card   bandwidth  GB/s  GB  CORES

-----  ---------  ----  --  -----

P4000      256    243    8   1792 

M4000      256    192    8   1664 

M2000      128    106    4    768 

K1200      128     80    4    512 

Oh yes, I've read forums all over the web and most of them have been useless because few people understand performance monitoring and tuning. My machine is tuned as far as it can go for the Library module so it is time to attack Develop. I'll stick my neck out and speculate that the determining factor for GPU performance with Lightroom is the memory bandwidth but haven't found a tool to measure wait times for that. If it is CUDA cores rather than memory bandwidth then going from the M4000 to the P4000 would provide a trivial benefit whereas if it is memory bandwidth then the P4000 is the superior solution.

Thanks,

Bill