I uploaded .mp3s of some files of my gt5 in action a while back before this discussion came about. My advice is this, these 2 units are completely different, to me the gt5 is more suited for live applications rather than for direct applications....IMHO the GT3 is more suited for this very application.
I'm not going into a "My unit is better than your's" argument here...if you want to find out the features of these units, go to the roland or any other gt3/gt5 website.
Also if you are thinking of getting one, go to the store and test drive one. Don't base your opinion of what you hear from us online...trust your own ears.
Having owned my gt5 for over 2 years now, or any
multi effects pedal...setup is very crucial, going from on amp to another can and does most of the time radically change the sound.
And also I do you use my GT5 preamp into the preamp of my current amp, I feel that it is best way to get the tone, but yes I do agree that putting 2 preamps together does screw things up a little, but with my amp it is not the case...I put the gt5 right into the amp's clean channel.
Fortunately my amp possesses a very acoustically
clean tone. I've tried the gt5 with a legacy too...sounded just plain awesome!
Another thing about these units is that you have to spend time...I stress spending a lot of time...tweaking the effects to your liking, bearing in mind that amp setup is crucial. The factory presets sounded like crap to me, but with a lot of patience and tweak, I love it now.
Chris.