I have steel shift forks and thats about it. Steel shift forks were a must for me because I've broken 3 sets of stock aluminum shift forks on various DSM's.
Other than that my transmission is basically stock. If you are looking at running consistent 11's you might want to look into a 4-spider center diff or a spool. I installed new shifter cables and haven't had any problems shifting at high RPM's since I installed those. I kinda wonder how much the double synchro 2nd really helps at the stock rev-limit. Now if you plan on revving her out to 8 or 9 grand, a double synchro 2nd probably ain't a bad idea.
As far as the GVR4 1st gear goes...I wouldn't mind a taller 1st gear but Marcus and others have destroyed the Gvr4 1st gears on hard launches. I kinda wonder if the EVO VIII 1st gear would fit DSM's. Its definitely taller. I know TRE sells their own 1st gear that is even taller than the GVR4 1st, but I haven't heard any reviews about it.