Yes they both will work. But I'd suggest getting a 7750. Doesn't use the power supply, and is lower power consumption and stronger than those 2 cards.
Sapphire 7750 1GB ($109.99, $99.99 after main-in rebate)http://www.newegg.com/Product/Product.aspx?Item=N82E16814102969
HIS 7750 1GB ($109.99, $99.99 after mail-in rebate)http://www.newegg.com/Product/Product.aspx?Item=N82E16814161403
Also, PCI-E 3.0 cards will work on any PCI-E x16 slots. And these cards won't have a performance issue on 2.0 or 1.0 slots.