My G5RV is only about 10' up in the air, so I'm expecting the vertical, with better feedline and proper radials, to outperform the G5RV.
Here's what EZNEC sez about 10m operation:
G5RV at 10': 7 dBi gain at 34 deg TOA (take-off-angle).
G5RV at 10': 3.2 dBi at 15 deg.
43' vertical: 6 dBi gain at 56 deg TOA. 56 deg is fairly useless on 10m.
43' vertical: 0.5 dBi gain at 34 deg. Same as G5RV TOA.
43' vertical: -6.7 dBi gain at 15 deg.
In the G5RV's favored direction, it is 1-2 S-units better than the vertical at the low DX elevation angles. Hope you are not expecting a lot of DX out of a 43' monopole on 10m. However, it should beat the 10' G5RV on some of the lower bands.