MacPro 3,1 (2008) logic board SAS connector: Has anyone "replaced" the stock hard drive backplane?
For changing the back plane you might look at the Pro Cable 1 with a review here.

There is also the DX 4 if you want to really stuff you Mac Pro with drives.

I don't have direct experience with a controller but was leaning toward a MAXPower RAID mini-SAS 6G-1e1i since it has both internal &amp; external SAS ports.  Note that this card will not boot the Mac Pro.

The real problem is that I would want both a RAID card and a Mercury Accelsior and the Mac Pro (2008) only has 1 free x16 PCI 2.0 slot and you would need 2.

There is also a rumor of a Mercury Accelsior with eSATA ports in the near future.