I have spent time with both frames. They actually feel more diferent imo than you'd think. I can see that they are based on the same idea, but there are important distinctions. Primarily the ommission of Woofer grommets in the Surge, you'll either like or not like, I happen to like it as it give me greater control/predictability on most shots that are flatter. The disadvantage is that it makes it less comfortable and dampened feeling, and since there is more dwell time with th Woofer System, you get a little more spin. The Woofer-less Surge also gives it MUCH more feel on touch shots, volleys, anything where you are not swinging hard.
Also the grip shape is quite squarish/boxy on the Surge, while the PD has a a more rectangular one. To me the PD grip is slightly better for semi-western and western grips, but you can get used to the Wilson grip too.
So I'd recommend the Surge to Serve and Volley/All-Courters, and Pure Drive to western-grip heavy topspin baseliners.
I have one Surge X with Touch Turbo 17 @ 58 lbs., and it is a tad bit too powerful, and another with Babolat Hurricane 17 mains, Wilson NXT 16 crosses, @ 60 lbs. , and it is just right.
I also sometimes play the Surge 5.1, but the Surge X has a slightly higer swingweight whcih I like, and extra leverage on groundies and serves. I have a 1 hh backhand though, so I am wondering if I should be favoring the standard length Surge, but so far, the extar .5" hasn't been much of a negative factor in any regard, including maneuverability, as the racquet is so light and maneuverable to begin with.
anyway, to wrap it up, these racquets are similar, but don't let people tell you they are clones, as they play pretty differently imo, and I'm glad I playtested them extensively before settling on the Surge.