I have a G90 in my UCD 3D. runs great but didn't like the 14x6 prop...very sluggish throttle response...but it did hover easiest with the 14x6...but for everything else a 13x6apc was happier on my engine. Quick throttle response for doing waterfalls or flips etc. I dont think I want any part of the OS91fx from all that I've read even if it does have a little more power..the ST90 is a good bang for the buck IMO. I also have a ST75 that I bought used from a club member that almost blows the doors off my 90. I did make the mistake of buying a Magnum61 fs...I think I'm sending this engine back to HP. Broke it in as suggested and it runs good but has no power, very low compresion. my .2$

Ron