Originally posted by eric_montgomery
I don't know what the Roland VG-88 can do. The only thing i know is that it's very expensive.

The VG-88 does:

Pickup modelling - P90s, PAF, Strat, Rickenbacker, Piezo and more
Guitar body modelling - solid, acoustic, banjo, resonator
Alternate tunings - any alternate tuning you like, plus pedal pitch shift (like a whammy on all 6 strings) - 12-string sounds, harmoniser and more
HRM sounds - not much use to you if you have the GR-33 - they're synthy
Amp modelling - same as the GT-3
Effects - cut down GT-3 - compression, wah, auto wah, EQ, modulation (tremolo, pan, pitch shifting, more EQ, chorus, flanger, phaser, harmoniser), delay, chorus, reverb and noise gate. All assignable to the expression pedal.

The GT-6 is a straight multiFX unit and very good too. As you have the GR-33 for your odd noises and synths, the GT-6 might be a better choice for straight guitar sounds, but the VG-88 is definitely worth a go if you already have the GK pickup on your guitar. I am very happy with mine.