I'm in the process of replacing my front and rear hub carriers ("uprights") with the EP uprights (20mm height drop front and rear), keeping the AP Racing 4 pot calipers in front (stock on my S240), but installing the "Lotus" AP Racing 2 pot calipers (44mm pistons) and EP parking brake calipers in the rear. The first pic shows the rear upright (and EP toe link), ready for the calipers. In the second pic you can see the new calipers. I haven't moved the brake hose over yet (that's next), I'm going to replace the stock hose with the Inokinetic QwkBleed hose routed above the upper A-arm, looks like the length will be OK.
As far as front:rear ratio is concerned, besides the rear caliper change (from the Brembo slider to the "Lotus" APR 2 pot caliper), I'm also increasing the rear disc diameter from the stock 288mm to 304mm. The fronts will remain at the stock 308mmm, with new discs front and rear (APR floating hat). Accounting for the disc diameters (multiplying the piston area by the disc radius), the stock F:R ratio was 68:32 (and that's best case, because it assumes the Brembo slider is 100% efficient, which isn't the case as Eldon pointed out). With these changes, my F:R ratio should be 58:42, which I'm hoping turns out to be a good target. I most definitely want to run the same pad materials front and rear. I'm hoping I can get away with not needing adjustable brake bias, but I'll do that later if necessary.
'08 Arctic Silver Exige S240