I shoot more 55 gr Noslers backed by 45 grs of Varget out of my .243 than anything else. Top accuracy with my rifle is the 95 gr Lapua Scenar and 42 grs of H-4350.
With respect to seating depth, every rifle is different. I usually try to work up a load with the bullet in contact with the lands. This is not possible with very light bullets like the 55 gr Nosler. OAL is 2.69" so you can see that only .080" of shank is in contact with the case neck. With heavier bullets that can contact the lands, once the maximum load is reached, I can work down from the maximum load to find the best accuracy load. If I think I need to play with the seating depth, I do that as a final step.
If you wish to feed your bullets from the magazine of your rifle, you might not be able to use this technique. If that is the case, simply seat the bullet as long as the magazine will allow, then work up your load.