It depends on what you feel is more important, using the mag or single loading only. Only your preference will matter, it won't effect anything either way.
If your rifle has that much freebore, then you can increase the powder charge until you get book velocity or pressure signs, whichever comes first.
Quite often near max or max loads will tighten groups up in belted mags, even with a long jump to the rifling, most of my 300's have extra long throats to achieve higher velocities in my 26" and 28" barrels, I normally load to within .010" of mag length and then try seating deeper by .005" increments until I find a good depth for that load/bullet combo.
You can of course seat to your preferred .020" off the lands and call it good, but there is almost always 2 lengths that will show an increase in accuracy, one close to the lands and one much further away, sometimes if the load is very consistent there can be quite a few lengths from the lands that work, experimentation is the key.