Thanks for posting contrasting line preferences. The new Trout Spey rods do have a wide grain window and it all depends upon your individual casting style. It is so difficult to recommend lines for a rod without observing the caster and what type and size/weight of flies desired.
I will test my rods with OPST and RIO
Skagit Trout lines with heavy flies and only a Polyleader and not with MOW tips, this is an interesting observation. Heavy flies require heavier lines to deliver the payload.