There is a trade off when you extend the travel on a axis. On X and Y it results in less contact with the dovetails therefore more slop in the table.
Best solution is to get a larger table and modify it to fit the X3 base.
I did this successfully on an X2.
On an X3 the column height is good and even with a vice I can't imagine needing more travel in that axis. It would mean you have to get a longer leadscrew but if you are going to CNC the machine then you might want to use a ballscrew so it is not a big issue.
cheers,
Rod
Perth, Western Australia