I run a FLI Atlas on my GSO RC10 and that works very well indeed. They aren't cheap but they are fantastically accurate and I use the same focuser on several different scopes.
At f/8 or f/9 the CFZ is not that tight. The main thing is getting a focuser that is rigid under the weight of your imaging payload - close to 10Kg for me now
Cheers,
Rick.