For a single CENTRALLY DRIVEN gantry I would not go wider than 600mm. Any wider needs to drive systems (one on each side). Yours looks considerably wider.

Furthermore, and critically, for your design it is very unusual to try and drive a gantry from one side only. It is very likely to rack / judder, plus give poor accuracy when cutting further from the driven side.

I expect that if you grab hold of the non-driven side you can push it back and forth several mm, maybe more ? If so racking is a the likely cause of the judder.

This can be reduced by spacing the X axis bearings further apart fore/aft, but I suspect even this may not be enough if you are still driving from one side.