I would put the RCS in the 10g. I would think that they would breed faster in a 10g than a 75g because of all the space. When I think of shrimp and tankmates I would never have something in the tank that can fit the smallest animal in the tank in their mouth. I hope you get what I mean.
hahaha i know what you mean man, i wouldn't mind to see some baby rcs get eaten by gobies but il consider your advice on the 10gal tank,
thank you!!