Re: Shred guitar specs?
While a Gretsch might have the flattest board, the upper fret access appears to be horrible (at least from a shredding perspective), thus you can't get the meedly-meedly up high as easily as with a JEM or Soloist.
A rounder-radiused board like a Tele or Strat would work fine, so long as the frets themselves were radiused flat, and the saddles were set to match the frets. However, this would leave pretty much a board full of speedbumps on the outer strings, so sliding could result in a sudden amputation.
If you want to see what makes a shred guitar a "shred guitar", compare the known shred guitars to the "standards" i.e. Strat/Tele/LP: flatter board radius, 25.5" scale, Floyd/Fender string spacing, etc.
Then go back and dig up some Gary Moore and John Sykes, and watch them shred on a fretless wonder LPC.