Very interesting. The 4X came out later than the 8X and Roland decided to add features the 8X didn't have.Hi John, I had a look at my FR-4X reference manual p.30 and is has "Changing the Pitch of the Tone in Octave Steps with the Right-Hand Keyboard - The key range of the right hand current part can be moved one octave up or down."
The FR4X seems to have more live performance flexibility than the FR8X, but the FR8X has far more capability/grunt.
I am surprised that Roland has not made Octave -/+, turning speaker on/off etc. easier to access.