Hi, 4X4Dragon.
I think it is a personal thing when deciding between 20IMS and modded Minimag stock reflector--if you take a look at the beamshots between them at section 4 of
Dummy Reference Guide to Minimag Mod, you could see that modded stock reflector will give a 'tighter' spot with tiny bit less of brightness than the 20IMS, but at the same time the self-modded stock reflector will have a brighter corona(as Nikon said).
I think how the well the self-modded reflector works will largely depend on how is it being modded. But for the work required and performance wise, I do agree with Dat2zip and think that 20 IMS is pretty easy to mod and result is great.
I haven't tried working on a McR20, but I did hear many good things about it and it probably would worth the try. /ubbthreads/images/graemlins/smile.gif