All the presets on eventides are totally tweakable, meaning you can edit all the parameters in whatever fx modules are involved in the preset/program.
As for live situations, there is a 1 or 2 second delay in switching from program to program, but you can set up your presets where you have all the fx modules in one program for whatever song you are playing, and then set each of those effects up so you can switch them on/off with your midi foot switch controller. There is no delay in this.
So you could easily have, say 6 or 8 (or more) effects that you can simply switch on/off in one program. It's like a virtual pedalboard. Know what i'm sayin?
But the power in the eventide is that you are not limited or stuck with the presets that come on it....you can literally build your own fx from scratch and create sounds that noone has created before.
The GTR4000 to my understanding is the unit to get if you play guitar because the presets are made with the guitarist in mind. You wont have to tweak as much to get a great guitar fx/sound, unless you want to create your own presets.
with all other fx units, youre stuck with the algorithms they come with. But some ppl don't mind this.......i hear the G-force is a great unit.
If you don't think you'll ever create your own fx or presets....then the eventide may be overkill for you.....you would be satisfied with the G-force.
But eventides are beyond everything else because you can go past the presets and make your own unique fx.