With these settings, I have 900 K GPU
setx GPU_MAX_ALLOC_PERCENT 100
setx GPU_USE_SYNC_OBJECTS 1
yacminer --scrypt-chacha -R 2560 -g 1 --buffer-size 2560 --lookup-gap 8 --worksize 256 --gpu-engine 1020 --gpu-memclock 1500 --temp-cutoff 95 --gpu-fan 0-100 --auto-gpu --temp-target 85 --temp-overheat 95
3GB memory GPU
Saphhire 7970
I actually found at NF=15 that LG=6 and LG=7 yielded faster hash rates than LG=8 for my cards. I would try settings for LG=6 through LG=10 (lowering or raising R to compensate) and see what yields the fastest hash rate for your card.
LG R
6 1883
7 2214
8 2560
9 2730
10 3091
Best speed 1.1k GPU. 7970 3 MB
yacminer --scrypt-chacha -R 2214 --buffer-size 2590 --lookup-gap 7 --gpu-engine 1050-1100 --gpu-memclock 1500 --auto-gpu --worksize 256 --temp-cutoff 90 --gpu-fan auto --temp-target 80 --temp-overheat 85
Total 3 GPU 3.32 K / h.
Consumption 385 watts from the wall.
I think it is not very economical.
Maybe you should think about buying R7 240 4GB.
Some would you share what makes a hash R7 240 4GB.