The differences between Pro and Free are slight and mostly invisible (except for some visuals), but under-the-hood Pro should find more sources through more connections, and thus increase the chance of faster downloads of popular content. So, I guess it would be very difficult to be sure if the a source wouldn't be found using the Free.

Anyway, Pro claims sound like marketing hyperbole: I think of Pro as a donation.

9.1 eh? Did you see the 'fix' in the sticky thread above your post?