I've hit with both sticks and feel the YTPMP and MGPMP are pretty close in stiffness, venturing to say the YT is a tad stiffer if you had to twist my arm. But I've only demoed the YT for a limited time so I can't really make that call without a little more play. I do vaguely recall reading a couple of reviews on the forum that says the YT felt stiffer compared to the MG, if that helps at all.
Supposedly, the technology behind Youtek is that the racquet stiffens more as you swing harder into the ball but lessens for those touch shots. To me, the MG is a pretty stiff stick anyway. But I really don't think there's going to be a huge performance difference between the YT and MG Prestiges. Specs have remained relatively the same and that's what really matters to me more than newer technology.
I don't think you could go wrong with either racquet though. The MG is a great addition to the Prestige line, and I believe YT version is going to prove the same. Out of curiosity (and without revealing your source of course) what kind of deal could you be getting on those MG's?