I've tried triggering soft synths from guitar via the MIDI out on my Roland GR-1. It's fairly useless. MIDI bandwidth seems to be just too slow for MIDI guitar, I'm assuming.

So I'm looking at the Roland GI-20 or the Axon 50.

The GI-20 (from what I see) uses old-school MIDI to transmit playing data. The Axon, however, uses MIDI via USB.

Is the Axon, with its' USB MIDI, any better than the GI-20 at reflecting the full range of what guitar-based MIDI is capable of? Or is my old GR-1 the culprit and much more is possible with a dedicated unit like either the GI-20 or the Axon 50?