After looking at my notes over the years and tring new powders ,I always count on
IMR 4064 for good results.
Unique and IMR 3031
I would look at starting with the 4350 with the .243. Much better velocity numbers particularly with the heavy bullets compared to Varget. Varget is probably my go to powder for 308 but I like h4350 or IMR 7977 in .243, 25-06, and 30-06. I've developed some great loads in 308 using IMR4064 and some great loads in 243 using hybrid 100v and IMR4831 among others. Like Jmr40, I try to use temp stable powders now as much as possible. I just don't want to deal with the changing point of impact because of the difference in temperature from Summer to winter here in Kentucky. I also shoot a lot when it's cold as well as doing load testing and frequently find my most accurate load near or above Max charge weights and I don't want to have an unpleasant surprise (kaboom) shooting a winter developed load in the middle of summer.I use H380 for 22-250, 4350 for 30-06 and .270, Titegroup for 9mm and .45, and I am about to start loading for a .243 autoloader, so I will start with Varget.
In early 90s 4064 went through some changes to make it cleaner burning.I have shot kegs of IMR 4064 in 30 caliber rifles and it is a great powder. But, it is long grained so I have used more IMR 4895/H4895 and AA2495 is the same, and used to be cheaper. The 4895 series throws better in a Dillion 550B measure.
But, I recently discovered that IMR 3031 is now short grained. It used to be long grained and all charges had to be individually weighed. This short grained IMR 3031 was an accuracy champ in the 30-30 and should be dynamite in the 223. I know the long grained stuff shot very well in a 308 Win M1a. I hope IMR does the same thing with 4064, been over seventy years since the powder came on the market, it is about time they improved it.