I'd say most NFL players on any given Sunday aren't 100%. If you're a great player, your 85% is probably still better than most of the league at 100%. If you're marginal like Deion Branch, your 85% means you're about to get abused...
In 2005, Branch started and played in 15 of 16 games. Yet, he still didn't even crack 1,000 yards. But that was one of Brady's best statistical years as he threw for 4,110 yards, leading the league in that category. Now, I don't know too many top receivers that played that many games in a season, had a QB leading the league in passing yards, but still didn't crack a 1,000 yards receiving.