I've noticed that unlike many other calibers, many .243s shoot better the hotter you load them, especially with the lighter bullets. Over the years I've had 5 (77, custom Mex. Mauser '98, Savage 99C, and my current Savage 110 and #1A). They all "like 'em hot."
Then of course there's TOO hot, but the brass tells you when it's hurtin' and to back off. At some point you would theoretically reach a pressure when it would be the bullet, the bore, or the action itself that would start warning you, assuming VERY strong ctg. cases. But I've never got there, even with my old '99, which was extremely accurate with 55gr. I just let the weakest link, the brass ctg., be my "canary in the coal mine."