Build for Under $800

[fcb]

He wants to play Skyrim and other RPG and RTS games. I know the 550 is better than my old hd5770 in some cases and it ran BF3 on high... So it should be ok with Skyrim on low or medium right?

I'm pretty sure you'll be able to play those games on medium settings. But I think it'll definitely depend on the resolution though and may have to turn off the antialiasing. It won't have problems playing titles like Starcraft 2 or Warhammer 40000 Dawn of War series.