Not sure what you mean by functional differences. There are some differences in the frame, slates, and other parts (like castings etc.) from one model to the other.
There are also some differences in the ability to adjust for level. I think the GC1 and maybe the 2's did not have adjustable feet. The GC4 had 22 slate levelers built into the frame but I'm not sure about the earlier models.
You might ask in the mechanics section for a more expert response.
OK. I'll duplicate this thread in the mechanics section is that is alright with the moderators.
Any functional difference between the models worth considering before purchase (used)?
Here's all you need to know....ANY GC can be made to play perfect.....or like shit...no matter which model, the future of any table you may end up with...is DETERMINED by who you decide to have work on it...period!
Glen