R7 240 4GB = 984 H/s
You're a little low, may want to work on settings - try a lower LG or increase frequencies. You're leaving hashpower on the table...
R7 240 4GB = 1.18 KH/sec
So 240 4gb and 750ti are 2 most efficient cards to mine yac right now?
I just want to try the coin especially with much greener setup.
From a price/performance ratio, yes.
The R7 240 4GB can be had for ~$70-$80 and draws 25W under YAC mining load
The 750 Ti is $130-$140 and I understand is around 35W under YAC mining load
If you
just want to mine YAC, go the R7 route. If you want a card that is good for a lot of things that happens to be decent mining YAC, spend more for the 750 Ti.
My 6 x R7 240 4GB rig is running at a total of 300W. It is 80W without my GPUs running. Therefore, I'm getting ~36W per card on average, but I think I am paying a price from trying to cut corners with an inefficient PSU.
The R7 240 4GB is great at mining NFactor 14 too. Perhaps, the multipool(s) should be specific to the GPU, ie a 750ti multipool, an R7 240 4GB multipool and so forth... paying out in YAC only of course.