It's not a question of 'over lining,' but a question of the number of 'grains' a line has vs the rod/size of flies you'll be tossing. Add to that will you be casting 'tips' of some sort.
Almost all 2-handers have a 'grain range' that the rod will 'comfortably' handle. This can be pretty wide for a given rod. If you want 'more grains' choose a line at the top end of that range or one with a shorter head.
While on the topic, a given line type will also help you load the rod even if (several) lines have the same number of 'grains' in the head/head length. Skagit heads will generally run (recommend length) at 2 to 2.5 times the rod length, Scandi's 3 to 3.5 times the rod length, 'mid-bellies' 45 to 55 foot of head, etc., and etc. This is even getting more interesting as a few line makers have come out with 'compact' this's and that's.
Hit RIO and Airflo's web sites as (RIO for sure) have a recommend list of lines for a wide selection of rods.
So the choice of lines can/gets pretty damned expensive to experiment with your credit card. Not sure where you live, but if you've access to a local group/folks that have a selection of lines you can play with on the river, all the better.
"One man's feast is another man's ......"