I would suggest getting the standard 2GB 7850. The $10 or so difference is worth the extra GB of VRAM. Maybe also swapping to a brand like Sapphire or Gigabyte, XFX arent really known for the graphics cards.
Both are about the same feature-wise, except the ASUS has support for dual cards (but considering the PSU, dont think thats an option anyway).
The AsRock is full ATX size and has two more SATA III ports. Because of that I would get it, but you wouldn't go wrong with either.
Yep, all works and none of the parts are objectional.