I'm sure it will be fine. Winchester brass in 9mm has been very good to me.
.755 is a great target, if all of your 9mm brass was .755, your accuracy and function would be superb.
Chambers in most 9mm combat arms are generous, and long with long throats and leades (Possible exception:CZ, they have been known for short chambers and rifling almost immediately after.)
I don't think there's a magic number as far as too long. I would assume accuracy would start diminishing when the case length got too long, but that would depend on the gun in question, a match grade gun might be better off at .755 than .760 or longer, but guns with long chambers may benefit (Better accuracy.) from the extra case length.
Too long, and the gun may fail to lock up, put rearward pressure on the extractor (Bad for the claw.) or exhibit other symptoms.
Make sure you gun doesn't fire when out of battery. (I doubt that moderately long brass would cause an out of battery condition, but theoretically, it might.....)
I'm prolly making way too much out of it, if your gun likes it, shoot it.