Stell frame cnc 1500X1000. Adjustable table your opinion please

[JAZZCNC]

Any of these are strong enough but the design can be simplified regards building and be just has strong. No time at moment to get into full debate about why etc but here's frame I've drawn that's similar.

Main points are the sides and Bed are welded flat has separate units then joined together with end braces etc. The Bed being a separate unit means the outer frame pieces support the bed material at the edges, the way yours is drawn the edges will be unsupported and could bend or flex under cutting conditions.
Lower diagonal braces help keep machine frame square and stiff, remember it's not just strength you have to consider there's resonances to deal with and bracing helps reduce resonance.

Welding major parts in sections on a bench then either welding or bolting together is much easier than struggling trying to weld individual pieces together and keep every thing sqaure and flat, aligned etc.

One other note.!! On this design the top rail extends.? This is to make full use of the Bed without wasting material having the bed/frame longer than needed which can't be used.