Richard.
First let me say this so there is no confusion, the effects in the GP-10 are typical Boss pedal effects quality. I wouldn't waste time doing A/B comparisons with my rack gear because it's not even close. Think of comparing a Boss pedal like the CE-2 with the chorus in your MP-2. Are they close? Not even in a thunderstorm.
This does do some modelled guitar sounds with certain synth combinations as I mentioned earlier, and these guitar tones actually get in the way of the overall sound when I have my actual guitar tone mixed in, or split to a separate amp. I'll need to edit that out. The reason being is because with the modelled guitar tones it's set to one sound, one pickup, one voice. Switching pickups on my guitar does not change the sound of the modelled guitar. I suppose in a limited number of situations that might be a good thing, but for the most part, it gets in the way. These guitar sounds only come into play when I have the 13-pin din cable connected.
I would need to use the 13-pin cable if I wanted to do alternate tunings, or simulated capo tunings and then the guitar works like a normal guitar, meaning it isn't modelled, just processed. Listening to it by itself, I can hear a bit of a difference from the original guitar tone, but in a live mix, I think that would be hidden a bit more.
Speaking of a journey, last night I was trying a couple more guitars in the GP-10. I tried the seafoam green one in it, and it definitely comes through with it's own personality. That one is a perfect guitar if you want to cop SRV or Eric Johnson tones. Definitely a Texas Blues guitar, so that didn't last too long. Then I picked out my 1983 '57 RI Strat and took that for a ride, and I think I'm the one who went on a ride instead...right back down to the early eighties again and this time I was having a blast playing I Want A New Drug, and Working For a Living by Huey Lewis and the News. I was in the "Crunch 2" preset with the boost and chorus w/delay effect added and I was nailing those tones to the wall! That was so much fun because I haven't played those songs since 1986. I think both of my 1983 Fender guitars might be the best ones out of all of them. The crunch tone was definitely there, but with a lot of clarity and articulation. This tells me that there a lot of possibilities with this pedal to get some really useful live tones. It has good clean tones, and it has good crunch and distortion tones, so that's a start.
As we both said, I may not be able to get away from the hybrid rig concept to get good articulation between the guitar and synth tones. That could happen with a very small rack that has an extra power amp and one of my Rane SM-26 mixers in it. Send two feeds to the guitar cabs and two feeds to the synth cabs with level and panning control for each. Oh well...there went the fly rig idea