Nice looking bike, you may find looking for a STX RC RD can be a pain ( it was for me a few months ago), so consider looking at the 730 series XT RD's ie, 732, 735 739 as they wouldn't look out of place on it and may be easier to find. The standard STX stuff while I like it wasn't as nice as the STX RC IMHO. I read something a long time ago that STX was Shimanos first offroad only built group, everything else they had at the time had trickled down from their Touring groups of the past.

Glenn