Another 7970 question..

Hi,
I've been tasked to build a dedicated password cracking system for work but unfortunately I've not been given very much budget budget

Fortunately power costs, air conditioning, space and looks are not an issue for my solution.

After reading around on the forums I've decided to build an open air system (something like this) using risers and four 7970 cards.

I intend to use an existing motherboard, RAM, CPU etc so no cost their.

I've also got access to loads of standard power supplies - has anyone had any luck in using an Add2PSU to link them together? That would save me from buying a high power one.

As I'm not going to be putting the cards into a case, I guess it doesn't matter if they are reference models or not?

If that's the case, I've got quite a few 7970 cards as an option for me ranging from £200 - £400 (link to dabs).

Will I have any problems going for the cheap MSI AMD Radeon 7970 1050MHz 3GB cards for £244 rather than a much more expensive one, such as the 1100MHz Asus for £359?

Thanks for any advice.
D