I am also looking for a CPU, so should I go with Athlon II x4 435 (overclock it to 3.4 GHZ) or should I choose Phenom II x2 555 BE (unlock it to a quad and then overclock) instead ?
In general the DDR3 is faster (measurable). If strictly for gaming get the 555BE (not guaranteed it will unlock) more general use the 435 better at multitasking.
I would take an Asrock over Biostar.
Best at gaming 555BE then 720BE. The 635 is good to but is better for multitasking and multi threaded application. I personally would choose the 720BE or 740BE if I was building only for gaming today.