Great link, thanks!
Started looking at the rears, and will have to read that link with more scrutiny, but I found the 135i rear rotor dimensions here:
Stock:
Based on those numbers, the rear disc should be a direct fit onto the 3.0si rear, but increasing 294X19 to 324X22. In trying to keep with similar front/rear bias, I wil lhave to see what caliper can swap over without it being the super expensive 135i setup. I haven't found any OEM rear calipers that "look good", thus the rear swap would be more for bias correction (and the fact I need new rotors anyway). What I don't have is the 135i rotor inner diameter for the parking brake. Will do more research...