I think if you're attempting to nail tones from John's past, that impulse is just simply not going to achieve it. It has nothing to do with who's hands are playing the guitar. That impulse is blocking a ton of upper frequencies that were present in John's tone on many recordings. It's just very possible that John is going for a different sound for this recording.I'm gonna go ahead and say between FAS and JP, the safe bet is that the cab sounds exactly how they wanted it to. Perhaps the issue is that none of us has John Petrucci's hands or can play as well as he can...?
I suggest trying to incorporate that impulse and attempting to dial in some of John's previous tones. You're going to have a VERY difficult time getting even close compared to lots of other available impulses.
The funny thing is that John is supposed to have a VERY specific micing technique that I am VERY aware and knowledgeable about, and he has stated that he has used this technique on many previous recordings. As Shredi stated, looks like we'll have to wait and see how is tone sounds on this new album.