True what you've said about the hearsay bit. I've heard a lot of mixed opinions so I wonder if anyone had tried mixing brands together and gotten it to work. I don't really mind getting my hands on any 7950 as stocks are so low and I've already made an initial investment on a MSI 7950. You helped, thanks for the reply!
The brand doesn't really matter in the sense that certainly the MSI & Sapphire will be fine together, just as the MSI & Asus or Asus & Sapphire would also be fine.
People just recommend brands they've had good experiences with, or what has better cooling and will survive overclocking and running 24x7 better, but this is all just based on peoples individual opinions. It would be hard to objectively tell them apart though because some people have really good experiences with one brand while others have the exact opposite experience, and so a lot of it is just hearsay.
Hope this helps!
Have you tried mixing brands or heard of anyone mixing brands and working?

Thanks for the reply!
No problems mixing cards.
BTW, I own 4x Sapphire HD 7950 (Dual X) and they work perfectly with a nice O/C.