For 75 grain bullets, H4350 and H414 work extremely well for me with nice nearly 3500 fps velocities. IMR 4831 and Sierra HPBT's makes for accurate shooting, and H414 and 55grain bullets cross the screens at over 4000 fps, and are absolutely devastating to varmints, esp crows who look like black puffs of smoke on impact.
I have never had great luck with propellants that fall on the faster side, i.e. 4064, 4895... Although I do like 4350 very much, I would take H414 over it for .243 use. One observation I have made is a mag primer has always been more accurate for me with H414, so regardless of temps I always use them.
My .243 is a bull barreled Mauser varmint rifle, so 85 grain and less bullet weight loads is pretty much all I add here, but I did load for a friends 788 using 100 grain Sierra's and IMR 4831, and it was nearly a one holer @100 yards. Man those Rem 788's are ACCURATE, and regardless of make, It seems the .243 is just an inherently accurate round.