I can't tell you about the difference between their "mid" line and their "top" line, but I can attest to the difference between their "top" and "I'm cheap" line.
About 3-4 seasons ago I bought one of their top end jackets. I've never once looked back. It is the warmest, driest and most convenient jacket I've ever owned. Even last week in Summit County when the wind chill was in the -30 & -40's, my core was quite warm. In fact, the "problem" with the jacket may be that it is "too warm." The zipper vents (in the arm pits and on the back) generally help, but today I had a baselayer, a midlayer and the jacket (it was high 20's - low 30's with no wind at A-basin) on with my helmet fully vented & even wearing my lightweight fleece gloves - and I was still a bit too warm.
Now compare this experience to the Spyder pants that I purchased the same season a few years ago. I skimped on them and bought the cheap ones (after unloading that much dough on the jacket, I thought it was justified). The wind cuts through them like nobody's business. They're generally waterproof, but I wouldn't stand in front of a garden hose with them (I would with the jacket). And they're cold. I *always* wear at least one, and often two more layers on my legs than I do on my upper body - primarily because of the difference in performance between the respective outer layers.
Anyway, long story short, there is a *huge* difference between the Spyder low end, and their high end. I would suspect that the "mid" range stuff is somewhere between what I've found at the ends, so yeah, there's probably a difference.
That being said, my guess is that unless you get cold easily, ski in front of fire hoses, or just stay out in conditions where 95% of all skiers stay home - the mid flight ones should be good enough.