Indeed, a 3.07 ratio would have been a good compromise, but for the E23/E24/E28, that ratio only came in the large-case diff, which was Euro-only. Not only that, a medium-case E23/E24/E28/E30 diff weighs 80 lbs, but a large-case diff weighs 100 lbs. Besides, I already had the 2.93 sitting in the garage!
Oh, yes, a 6-speed would be nice, but the only 6-speed that bolts up to the M30 engine is the E34 M5 6-speed, which is as rare as hen's teeth!