Posting result if anyone else is looking for 1080p short throw. Optoma got back to me. Their recommendation to replace the Optoma GT750(GT750E) is to go to GT1080Darbee which is short throw 1080p with similar characteristics. IT's list price is $650 usa.

Project Central .com has a nice projection calculator where after finding your projector you give the size dimensions and it tells you how far back to have the projector. For 16ft wide by 9ft high it says about 8ft.

I may not choose to upgrade after this anyway. Our purpose is to use the LM for training and we don't use the simulator games. We just use it on club fitting and range. Plus I have a impact screen so it probably doesn't matter going from 720p to 1080p for this purpose.

If you are using the FSX games then I heard the graphics are worth it.

I was don't it but I asked anyway if Optoma had a similar short throw in 4k. They said not yet.