Well allow me to answer that, seeing as it's something that I wanted to know myself (owing and loving the original). I only tried the GT briefly but it didn't take me long to make my mind up.
To me it was a faff to use in comparison, thanks to it's not very well laid out "dual" architecture. On the original it is direct, immediate and logical. On the GT it is none of those things, and the godawful colours do it no favours either. The GT *should* have been better, but it just wasn't. Of course sound wise they are the same, but that's not the issue. You also lose the D-50 option on the GT, which may or may not be a bad thing
But, it is no doubt a fine instrument and indeed sports more power than the original.
If you're happy with the GT (and its shortcomings) I wouldn't recommend getting an original. My 2¢