You apply 2 queue per GPU, right? Make please option for switch between old/new modes for selected card. For example - like "dev=0,1,2" for old mode and "dev=0,0,1,2,2" for new mode (card 0 and 2 - 2 thread/GPU, card 1 - 1 thread/GPU)

Also, with v6.1:
gtx750 - SM5.0 - same performance, +1..2 sols/sec
gtx950 - SM5.2 - yes, +2% faster
gtx1050ti - SM6.1 - 1-2% SLOWER 

Rollback to v6.0