I would go for a larger table, you can start with a smaller mat and go larger at a later date if you want. I think having extra table space is ALWAYS a plus, it gives you a place to stack your cut fabrics, blocks, supplies, etc.
If I remember right, there is a website that will make cutting mats any size you want them. I'll go get my friend Cindi, she's ordered from them in the past. Standby....