The obvious and simple answer is yes, he raced for a long time at the highest levels of competition, so his 1:42.60 AR in the 800 was his full potential.
Nonetheless, I have to wonder if his AR was his maximum potential. Looking back at numerous runners, peculiar circumstances (e.g., injuries, poor racing tactics, untimely death, etc.) made you wonder if they ever performed to their full abilities. Jim Ryun and Steve Prefontaine immediately come to mind.
Gray was a little before my time, so I don't have much knowledge of him. What I have heard several times is that he had tremendous leg speed, tended to be a front runner, and ran poorly tactically in major races. This makes me wonder if his best performances -- for someone of Gray's caliber -- fell below expectations.
What do you think?
BTW, does anyone know Gray's 400 and 1500/mile PRs? I can't find them.