In general I'd say that the PurePitch packaging has yielded more yeast growth than I used to see with the vials. I say that because of how much yeast I've dumped from my conical post fermentation. However, I had a few packs from late august this year that seemed to underperform comparatively speaking. At least that's my impression... I have my first stalled ferment from that batch. I just made a small starter from a new PurePitch pack today that I'll pitch in hopes of further attenuation.
So, while I have nothing but observation to back my comments, I would say that I've been thinking there's some differences for sure. My feeling is so much aligned that way that I'll probably be using Wyeast for a while.