Yah, I was waiting for someone to catch onto the 930 version of the 915 being 4 speed
The Carrera G50 (mechanical clutch) is on hot demand from people trying to put them in earlier 911s that came with 915s... 911 guys seem hard on the 1st gear synchros.
Having a '79 911SC with the 915 tranny I can vouch that it is a smooth tranny when properly used and with the right oil in it.
Due to the aerodynamic limitations of the Beetle platform I think it is a lot of extra cost and effort for a 6th gear that is hardly needed. IMHO
Good Luck,