At last I got the numbers. A combined hashrate of 77.24 MH/s with a decent efficiency of 0.44 MH/J. GeForce GTX 1660Ti is quite able as a sidekick. I could have don't
GeForce GTX 750 Ti 2Gb : CUDA: failed to alloc memory (version v0.5c) · Issue #13 · kozyilmaz/nheqminer-macos · GitHub
MSI GTX 1080 Ti Gaming X Mining Performance Review - 1st Mining Rig
Ravencoin (KAWPOW) NVIDIA and AMD overclock settings for GPU mining | NiceHash