Buying new Graphic Card

Hi, I amb looking for a GPU graphic card to start playing modern games in my computer.

My specs are:

AMD 440 X3 processor
ASUS M4A88TD-M EVO/USB3 Motherboard (with an integraded Radeon 4200 graphic chipset which I am currently using)
4 GB RAM DDR3 (Kingston 1066 MHZ)
600w Low-Brand PSU (with extra connection for graphic card)
1 TB SATA3 Western Digital Hard Drive
23-inch LCD Display Monitor

I'd like to play mostly strategy/rpg games (X-COM, Starcraft 2, Mass Efect 3) with decent to great graphics (and 1900x1200 resolution if possible), and maybe some FPS with lowered graphics.

I have been looking at two Radeon cards, the 7750 and the 7770.

85 euros

105 euros

Will the 7770 be bootlenecked by my cpu, or is it worth buying it?

Thanks in advance