Thanks Jazz.
I have made a few changes since I posted that last image...the main one being the removal of the single leadscrew option. I've decided that I want to do a decent job of this, which means it'll take me longer to get it running - but the end result will be worth it...so dual leadscrews from the start - hopefully driven from a single motor.

I'm still very much tinkering with the overall dimensions - I have shrunk the z depth & reduced the overall height a bit as well.
I hope to have a bit more time to spend on it tomorrow to make some more changes, then i'll come back for another slap on the back of the head :-)

On the gantry you posted above - I assume that the spindle mounts between the *ahem* open legs?
Question...does the distance fore/aft that the spindle is mounted (relating to the x rail bearings) have any effect other than allowing the cutter to reach different areas of the table?