I shoot a 6mm Remington, which uses the same bullets, but has a larger case, so powder burn rate and pressures might be different for optimal performance. What weight bullets do you intend to shoot?
I shoot little 55 grain Nosler Ballistic Tip varmint grenades at 4,100 fps with Varget. The heavier stuff, 90-100 grain target and hunting bullets, I am currently loading with H-4831SC at about 3,100 fps for the 90 grain Berger target bullets. My barrel twist is a bit slow at 9.5:1 for heavier bullets than 100 grains.
A quick perusal of a couple 6mm websites where both the 6mm Rem and the .243 Win are commonly discussed seems to suggest that powders that work well for one will work well in the other. I've also had some success with Win 760 and IMR 4350 with this particular rifle, but Varget and H-4831SC are both working well for me in both velocity and accuracy. I just last weekend shot a 4.115" load development group at 400 yards, just playing around with the Berger 90's and 46.6 grains of H-4831SC, and have not really worked the load up yet for max accuracy.