8x2GB or more.
Quad sets (4x1GB and 4x2GB) minimum
A "bank" is all of the DIMM slots on one channel or Riser.
Dump the 512s
A set of 6 DiMMs is not symmetrical
Amazon has 2x2GB FBDIMM 667s $39 which is why I (and others) have gone.
4GB FBDIMMs (as in 2x4GB set) cost too much
www.macperformanceguide.com has a lot of good tips about CS6.
They are top quality brand name... not a big market of us using older Xeon FBDIMMs.. who knows. I wouldn't be using and recommending if I wasn't okay with them. And I've seen a ton of issues with OWC and having to exchange now with FBDIMM issues on 1,1 thru 3,1 models.