I have a GK on my frankencaster tenor guitar made for me by Soares-y with 4 Deusenberg multibenders and 4 d-tuners. (insane number of open chords possible). I find it tracks beautifully. I am currently playing it (through the standard foot thing, with those sounds like a bad computer game in the bedroom next door) into a Waldorf Streichfett. The bends go through great independently. I'm not playing fast though as it would sound faintly ludicrous. I have a MidiPal doing its arpeggifier thing as well but it occurs to me I haven't done them simultaneously (retune in mid-arpeggio) because I have been using its tanpura setting almost continuously into the Streichfett.
Metheny in one interview talked about how the guitar synths were better pre-MIDI and made reference to some model numbers in the way that people do. He was probably referring to the VOX V251 Guitar Organ.