If possible, put one end of the table against a wall. That give you the most room at the other end to walk around the table and have space for a table, chair or whatever.
I have a room about that size. I put mine against the wall for the lighting situation I have. You could have it in the middle of the 20' length but you would lose a lot of room for other furniture, etc.
Width wise, I feel like I have plenty of room. The quilting table is about 4' from one wall, then the width of the table and I still have room for a table against the other wall and a good-size walking space between the table and quilt table. Hmm, haven't measured in quite a while maybe my room is a bit wider than yours.
Good luck I know you can make it work with your space.