Only you know what space works best for you and the type of sewing you do.
Some people sew in very tight spaces, and are comfortable.
And some can't function without lots of space.
My suggestion to you would be to try it! .... perhaps take one of your current tables and measure out the smaller sizes you are considering ... then put a barrier to keep you with in that space and see how it works.
Another possibility ... could you L the tables for your machines, or put them back to back, so the space does double duty for both machines?