I didn't have the guts to test HA SSO on 7.4.100.X and 7.4.110.X, however, I am currently using 7.5.X.X in production. We would regularly (as in once a month) do failover in the middle of the day and no one would see any impact.
Why do we initiate a failover? Because we can. No joke, because we can. Really!
Currently Cisco recommends v184.108.40.206 MR1 for AP SSO stability. You only use v7.5 if and only if you need a feature that v7.5 offers. Some of my clients are on v7.5 due to that reason, but again, it's what suggested by Cisco.