All I can say is I played through a 505 once. It's a $50 toy, and sounds terrible. *I know Zoom has a really bad rap to overcome.
The GFX-8 is in a different class. *It's a bit underpriced for what it can do. *I know Harmony Central reviews can be crap, but there are plenty of glowing reviews there. When I was shopping for a multieffect board, I didn't have a price constraint. *If the GT-5 would have done what I wanted, I would own it.
The GFX-8 isn't perfect. *You can't change your effects route. *You are limited in your choice of effect combinations. *There is a *very* brief but noticable cut out when switching patches. *If I didn't care about the distortion/modeling, I might have gotten the GT-3...but I hate the Boss data wheel! *For me, the amp modeling on the GFX-8 was the major selling point.
The guitarist is playing through a Legacy half stack, and I have no problem cutting through or getting good tones with the Zoom through my Mesa Mark III
. The Zoom unit's amp "models" sound great. *I can easily make the Boogie "close enough" to a Fender, Marshall, or 5150. *The Recto model doesn't sound good through the Mark III...but I can live with that. *The reason I'm so enthusiastic about the GFX-8 is that it doesn't kill the sound of my amp. *I still get all the depth and punch of the Boogie--just with a different character. *If I turn off all the effects and just use the modeling, it sounds incredible. *In fact, I use it that way a lot. I have absolutely no regrets. *Right now I don't know of a better floor unit for my purposes.