750 is better than 500 in an 8 week cycle, no doubt.
Did you frontload?
I do think prop is better for 8 week cycles but not everyone is keen on the frequent injections and the low concentration of the drug (requiring larger injection volumes).
Regarding when you saw favorable results, that's a very individual thing. Of course the whole reason to use these drugs is to get results, so do you what you have to, ya know?