Personally, I'd go with curves as wide as possible. My 70' passenger cars from MTH look OK on 0-72. Anything longer would look silly, IMHO.
Can you go with a wider table? Maybe 9 or 10 feet wide instead?
If not, a 96" wide table can accommodate the 76, 80, 84, and 88 inch curves that you can get from Gargraves/Ross.
When I built my current layout, I thought 0-72 and 0-64 were the bees knees. The biggest engine I had at the time was a Lionel scale NKP Berkshire. The next "table" will allow for 0-96 and 0-84 instead.
On a positive note, almost everything looks better running on wide curves.
