After some heavy debating, I have placed an order for a 2000 Viper GTS to replace my M. It was lots of fun while it lasted, but I'm really looking forward to experiencing the Viper. I don't expect to take delivery for another 6 months, so I'll have to cram in as much top down fun as possible. Not to worry, I'll still be reading posts here for a long time to come (hell, the board is great fun). Thanks for all your help!
BTW: I'm entertaining offers on my 2000 M immmediately. Figure ~40K or o.b.o. Estoril Blue/Estoril Blue/Black. Premium warranty (all 2K BMW's got them), matching hard top, and Z3Solution Stone Guards.