I have run my S90K for years on a Zinger 15x6 prop... so I can safely say than using a prop this big will not hurt the engine. It runs just excellent... it may even handle a 16x6 if you don't mind losing some power. Just make sure you have adequate cooling and the engine is set up correctly. I mean, use the right plug, don't run 20% nitro through it... that kinda stuff.

Can't speak for the G90 though, since I don't have one... but it shouldn't be all that different.