couple of things to think about, spey/switch rod weight is 3 line sizes heavier than standard single hand rods. aka a 6wt spey is right around a 9wt single.
then casting wise, it's super hard to make the transition to "under hand" casting because it's all underhand with your other hand vs using your normal casting hand which is only a fulcrum point in this style of casting.
that being said, once you figure out how to keep your dominant hand still, the skandi/skagit underhand cast with the proper shooting head on the rod. it really is mind blowing just how far you can cast with your back up against trees, rocks whatever(no back casting room).
as of right now, i screwed up when i bought my airflo rage head and went with a 450gr, when i should have a 525-575gr on it. i can still cast 80-90'. i cant wait until i get the proper line on my rod to see just how far i can throw a fly(though 80' is probably farther than i will ever need to cast lol, other than lake fishing...).
also the new casting style heads in the north west is "scandit" sort of a hybrid of the heavy skagit head with a bit of taper so it will have a bit better presentation than the "clunky" skagit(pretty much a no taper head that has the most mass to move the biggest flies) and throw large flies. but not as nice of a presentation as a "scandi" style head taper.
another option is to get your rod picked out, and call or email steve godshall, he's the most raved about custom line builder any where. 90% of the time he has already built a line for most rods and if not give him the specs, and let him do his magic!
good luck. DJ