Thanks everyone for the warm welcome!
And special thanks to everyone for the very in-depth, detailed replies which did make it a lot easier to make a decision. It seems the best option will be to save a few bucks with the "SnD" version and then spend those bucks on an RMX & possible expansion, heh.
Also, as Maldroth pointed out, I too was concerned about introducing a set of rules and then asking people to re-learn stuff, but since it seems RMX is far more compatible than I expected, I'll simply add a few things here and there from the get-go. Heck, it can't be more complicated than figuring out what the !*#^$! a sorcerer/monk/paladin/arch mage actually is.
I also want to voice my thanks to ICE & anyone involved in the project for bringing back the best system ever