I've heard some really negative feedback on the hybrid crossfire of the A series chips. the 650Ti would be the better option out of the ones you supplied you would also want to turn off the onboard video from the A10 when you upgraded to it. From what I've heard any mid level card will destroy the A10 in normal and hybrid.
I would suggest a hybrid crossfire. Let me look for that review I found before
It compared a A10 crossfire vs FX 4170 + HD 7850 vs i5-3750k + HD 7850 and the trinity crossfire enabled build prevailed all benchmarks.
And yes bigshootr8 is correct about mid level cards disabling crossfire. Hybrid crossfire is limited to particular discrete gpus, 6670 is one of them
for this build power efficiency is important, but I might be able to get more power, I'll have to look at what each of those 6 or 8 pins actually are and related to that what is the primary power source of a card with aux power the aux power or the pci power, lets say for a 125 watt card.