I was suprised I do not seem to be able to resolve Jupiters GRS, I can make out bands, but my 10" Dob does not seem to show the planet much clearer than my 4". The Cassini division is only just visible. However, I did find the 10" to be an amazing deep sky experience. Rather than stronger magnification, I found larger apature to offer unparalleled clarity. But, that's probably just me, that's why I am in this section
Maybe you could look out for a local Astronomy club, I beleive most hire out scopes, that might help your desicion.