Yet another thread about a new build

[RickC Sniper]

I am having a local shop do a build for me and I have a couple of questions. (Please don't tell me to build it myself. I can't. )

Case - Antec 300 Black Steel ATX mid tower.
HD - Western Digital Caviar Black 1TB
Video - Either an ATI 5770 1gb or a 5850 1gb depending on my budget. (ASUS)
Mem - Ripjaws series 8GB (4 x 2GB) 240 pin DDR 3 1600 CL 7-8-7-24
CPU - Phenom II X4 955 Black edition 3.2GHZ Socket AM3
MOBO - M4A79XTD EVO AM3 790X ATX AMD (ASUS)
OS - Windows 7 Home Premium 64 bit


Do you guys favor one video card maker over another? I was thinking an XFX or Sapphire card but the tech who helped me put this together swears by Asus. Does it really matter?
If I add a second gpu card in crossfire in the future would the Phenom II be overmatched?

The mid tower case could be an issue in the future because of the room for a different video card. Those two cards listed are about 9.5 inches long which is a lot smaller than other options. An 11 or 12 inch card wouldn't fit without some cutting.
If I add a 2nd card in crossfire in a year or so either of those cards seems adequate to me so I think the case is ok. (it's size and button locations are user friendly to me) Also, cases aren't very expensive.

Should I consider Win 7 Professional because of the "XP MODE" feature or is this pretty mute because I'm going with 64 bit?
I am currently using xp home 32 bit.

If anything jumps out at you please feel free to be critical.
And THANKS!