It's funny so many players say these discs are similar. They aren't at all for me.
I throw a lightly broken in PPD as my main deep distance driver, getting 350-400' in a mostly straight line (flips to flat, only turns over in a headwind) with a consistent but by no means huge fade at the end. I would compare it to a Star Destroyer in similar condition; I get similar distances on similar lines.
My opto saint pro, on the other hand, doesn't make it to 300' for me. It's still a very useful disc, that for me flies very consistent line (straight for a while, then much more fade than what my PPD shows--maybe not quite a meathook fade, but close). It's also very well behaved on landing, sticking more than skipping. I use it mostly for long upshots, since a comfortable throw with it is preferable to trying to crank my Buzzz as hard as I can. It's really not comparable to a regular Saint at all for me, I would rate it no higher than 4 in terms of glide. In fact I logged on today to ask how it compares to a Thunderbird, which I'm considering buying (in a new thread).
In short, my PPD is a very fun to throw, a distance eating monster that's still controlable, while my Opto Saint Pro is more like an accurate, very overstable fairway driver, which stays where you put it down thanks to its low glide. Not similar at all for me.