Do your ammo testing at the far distance you want to shoot. Prove it at 100 and tweak it at your distance. Then practice at twice your max distance if possible. I compete a lot and try to use 1000 yard line to make my 600 yard strings much easier. My success at 1000 is not as good as I want it to be, much because my choice of weapon, but the 600 yard line is easier than it ever was.
So I'd shoot as far as I can, but in the meantime fire a few shots at different yardages so you know where to hold. Learning to shoot way out there makes 300 yards a chip shot.
Finally dump the bench and shoot from field positions. Over my pack is the best. But learn to grab brush and use it, lean into it, use a tree for a back or shoulder rest, cross sticks etc.... Finally through all this you'll learn how far and what position you can shoot from.
In the off season, though the trajectories are often not quite the same, I'd make use of something like a 223 varmint rifle and shoot it a lot. It'll take 5-10000 rounds to toast most 223 barrels and shoooting them is cheap enough. Then when closing in on season you switch over. Much like I do. I have a very expensive AR15 in 22lr. Its cheap to shoot and I can use it in the yard each nite offhand. Switching to my real AR15 is not that big a deal later.
PS using a really good 22lr at 100 and especially at 200 yards is super practice for positions and wind shooting(learning the wind)
Jeff