First of all, Hi !
As far as you are satisfied with the 325 grain Scandi, what length is it?
I use different Trout Spey equipment from 11’ to 12‘6 rods and I have to say, a Scandi of 300 to 330 grain does it „nearly all“ in streamer size and weight for me, especially on my 12‘6 setup. Maybe not for the biggest mouse patterns...
What was already mentioned here, the short Skagit heads may be too short for a 12‘6 rod.
But they are adaptable very well with longer tips to any configuration you want! And the benefit is better turnover compared to a longer Skagit head and short 10’ tip, especially in the trout Spey category.
If you want something to complement your Scandi, don’t be in doubt with a short Skagit, to cast what you can’t or think you cant with your Scandi for trouts.
The OPST Skagit is a question of taste. I liked it turned around... Mounted as it should be, it got all the weight in front and gave a strange feel to me. As you already experienced, it is good for SH casting. I know it got a lot of followers also for DH use. Maybe it’s only me. I don’t like a tip heavy feel for casting and presentation.
I am using the Airflo Scout in different setups from 300 to 420 grain and love it. But it needs adaption. Tips of 10’ alone are too short, even for my 11‘ rods, at least for me and the distances I need/want. I use 12‘ to 15‘ tips. No problems with blown anchors this way. Distance, control and presentation will improve a lot too.
I also built pieces out of Intermediate lines to loop between head and 10’ tips for the 300, 330 and 360 Scout (length of 1m to 1,5 m in adapted taper and weight, depending on length-weight-ratio of the Head Front and the tip to „hit the balance“ in the middle).
This way it’s a very good transmission from the floating Belly to the sinktip of different densities, both for casting and fishing....
This way it’s possible to use Rio
Scandi tips of 10’. For casting and presentation I prefer tapered tips.
For your rod - if you are satisfied with rod load from your 325 Scandi - I would start with an Airflo Scout in 360 grain and 15‘ Rio
Scandi tips in #7.
If you choose the way of an Intermediate-„cheater“ between head and 10‘ tip, it would be the Rio
tips in #6. The 10’ and 15‘ tips of the same line classification are different in length-weight Ratio. The tips in #6 and 10‘ are comparable to #7 in 15‘.
It’s very nice casting for the heaviest of flies, also for distance.
And I guess distance and wind resistance matters for you. Otherwise you wouldn’t choose a 12‘6 rod.
Even with detailed suggestions you have to experiment what fits your needs and your casting.
If you want to choose the Airflo head, try at least two on your rod, because of production variations in length, mass distribution and total weight. In general, with the Skagit heads and it’s pure mass it’s not that critical, but for the lower weights as for Trout Spey it can be important for the casting characteristics.