The motor for head lift is just so your arm doesn't get sore cranking the heavy head up and down. It is not meant for fine feeding like boring. When not CNC'd the head should be locked as the screw likely has a good amount of backlash that could show up in the finish.When CNC'd, attention is payed to eliminating backlash, and to the dovetail slides. This is why a CNC'd machine doesn't need the head locked.
As for the 3 Grizzly choices, all are about the same physically but a few notes.All are about the same physically, but the 0755 head will tilt 90 degrees left, whereas the other two will only tilt 45 degrees either way. The 0761 doesn't have the x axis power feed and is a single phase motor. To me the extra $500 for the power feed, and VFD motor with the higher speed spindle on the 0762 is worth it for a manual machine. I happened to visit Grizzly while on vacation a few weeks ago and the G0762 really caught my eye. If I am remembering right it had a Hitachi VFD. If it were me I would get the 0762 out of those 3 choices.