IMHO Skagit heads equate to big heavy flies. Period!
Otherwise fish a Scandi/Skandit or something more pleasurable to cast. That being said, nothing turns over those big heavy flies like T-14! (work from the fly back. remember?) So,,, in order to turn over T-14, the tip of your Skagit head must have at least as much mass (wt/ft) as the tip it's trying to turn over. Make sense? Find out what diameter floating line it takes to weigh 14 grains/foot. That's your starting point.
It never hurts to go up from there. I tend towards the upper end of a rods grain window.
You will hear other people tell you they can cast big heavy flies on this or that head, and on T-11. But will the fly kick over & lay out straight,,,,every time? If it lands in a heap, you have no control of the fly until all the slack has been taken up. You don't know what it's doing down there. Mr. Steelhead can taste your fly & spit it out & you will never feel a thing.
I have no experience with OPST heads. No doubt their heads in the 575/600 grain range are up to the task. As to what will work on your rod, it never hurts to make a phone call. I do have experience with the original Airflo Skagit Compacts in that range & can assure you, they are indeed capable of kicking over big flies & T-14.
Enjoy your new rod & reel.