Varget's biggest claim to fame seems to come from the target shooters. Temperature doesn't seem to affect it. At least, not nearly as much as a lot of other powders. Important towards the end of a rapid-fire string as a hot chamber and temp-sensitive powders will make the shots start climbing on the target.
In a .243, I load IMR 4350 almost exclusively with everything from 75-105 gr. weight bullets, but then, the .243 isn't exactly my favorite round, and I haven't given loading for it a lot of effort.