See https://cds.cern.ch/record/2743157/files/Seeman2020_Chapter_... you can get better Q for superconducting linacs and also operate them in CW mode without fear of burning them up. Off the cuff I'd speculate that superconducting magnets that can support 2x the magnetic field might support 2x the accelerating gradient but we are talking AC operation here, not DC.
