Try to reduce the launchbound in Shabal from 320 to 256. If you have time revert some of the change sets to find the one that slows down.
There are to many changes for me to test ((
Did you mean shavite to change TPB from 320 to 256? (ccminer-windows\x11\cuda_x11_shavite512.cu)
Yes. The 750 has 512 shaders while the 750ti has 620. A threadcount of 320 was faster on the ti but proboby not on the 750