I've used H-4350 (E) for 338 , Win Mag and for 300 Win Mag-----both in model 70 Wichester rifles with standard barrels. IF---you load (or reload) to the maximum levels for a given cartridge and bullet combination----you can exceed the recommended pressure levels for gun/cartridge. While the load may be quite satisfactory for a cool/cold condition it may not be satisfactory for warm/hot conditions.
Actual example: While loading cartridges for the above, a near max load was chosen for both calibers. The cartridges showed no signs of pressure abnormalities when fired in Jan/Feb; however, when fired again in July/August, the primers showed a slight loss of radius at the shoulder where exposed at the rear of the primer pocket in the cartridge. Extreme in this case means that "within a limited temperature range", you will experience less of a velocity deviation than with standard powders of the same type. In my case; the ammo, being subjected to the intense heat of the desert sun, caused that (those) loads to encroach upon being "too hot"-----so, later, I backed the loads off a few tenths----the accuracy was still there and I've left the load unchanged since.
I do favor the "Extreme" powders---and I have noticed a difference over the older powders---(in the desert regions), but (I can't vouch for noticable differences in frozen environments, in Montana/Wyoming/Tetons)----------I've used IMR 4350, A 4350, & the old Hodgdon 4350--------If you run the rifle/load on the ragged edge, Murphy will find a way to mess with you.-----------I agree with BuzzBoss