I dunno Rob
I've compared C9.25 and C11 Jupiter and Saturn images produced by Damian Peach and I don't think there's a huge amount in it IMO
I guess if you were able to sell the 9.25 for a good price and have most of the cost of a good second hand C11 covered the switch could be justified.
I guess any increase in aperture and the associated light gathering and increased resolution has to be a good thing.
Any bigger though and cooling and seeing start to play a bigger role