I know a whole lot about stock E46s, modded (not prepared) E46, and quite a bit about stock E90 and E92's. Remember my sister has that E90 too.
You were the one talking about how the E92 is superior from a chassis and suspension design standpoint. All I can do is take your word for it.
How much have you driven stock M3's? Their suspension (rates and such) is all about compromise, and they really do have a great compromise between the way a suspension should act and comfort. But with that said, a stock M car will feel planted for petty corners, but when you really start throwing the weight around its going to feel like a boat.
Usually I'm in the "take your time, do it once, do it right" camp, but in your situation I say go for it before its too late.