I just got one. It's a bit of a bugger for HiCapa's (I knew that going into it).
With some work, a Serpa fits a 5.1 ok. It requires a reprofiling of the edges of the holster opening (I filed mine...took 2-3 tries and 15-20 min) to accomodate the width of the 2011 grip.
The way that it's molded...it will not nicely fit a 4.3. You would have to cut about an inch off the end of the holster so that the railed frame of the 4.3 would fit. Even then, once the 4.3 was inserted enough to lock in...about a 1/4 inch of it would stick out the end of the holster...kind of ugly.
Either way...you need to mod the trigger guard area of the holster...or the trigger guard of the pistol so that it locks into the Serpa. After looking at it, I opted to take an extra grip that I had and modded the trigger guard. Essentially I rounded off the square trigger guard to a more "normal" 1911 profile. Works like a charm.
So a 5.1 can be made to fit...a 4.3 not without some major chopping.