I have an older mother board (ASUS P5Q3 Deluxe) with PCI-E 2.0 slot and a 550W power supply.  I want to upgrade my GPU to a AMD 7850 850 MHZ or 920MHZ.  I'm pretty sure the mobo and PSU can handle the card but will my hash rate for LTC be slower than if I had a motherboard with PCI-E 3.0 slot?  Could it even handle a 7950?