7' vs. 8' vs. 9' vs 10'
From my experience, the game automatically gets tougher (skill wise. meaning stroke and envisionment) as the size of the table increases. As an example, I play in a 14.1 league once a week on 9' tables. I, also, play a friend 14.1 on a bar box once a week. Since Mid-August, my hi-runs on the 9' table have been 59, 43, 42, 37, 35, 33, and a slew of 20's. On the 7' they have been 72, 68 unf., 58 unf., 75 unf, 92, 100 out, and many 50's and 40's. With my eyes not as sharp as they used to be (diabetes) and a failing in my confidence, it is very obvious, without question as to which tables play the most difficult. Of course, the fact is how many players, today, have played on or have even seen a 10' pocket table. I've been playing over 40 years and the only time I've seen or played on one was at Tally Jenkins backroom in Pottsville, PA. (note that at Tally's, you had to be careful when you placed your stick down 'cause of all the holes and cracks in the wooden floor. Straight through to the basement!) So throw the 10' tables out of any comparison. And then you also have brands of tables that just play easier. I mean a standard Valley Bar Box plays much tougher than a Great American and a Brunswick plays tougher/truer than a Gandy or Olhausen. And the Diamonds probably supersede them all in any size.
Winston has a good analogy of the Baseball/Softball thing. But, beware as someone else eluded to, don't think you are gaining an advantage on a "player" in moving him to a different size table. The "player" will still find his way to "play" for the win under any condition. After all no matter the size of playing area, bounce off the rails, cut of the pocket or rules of the game. Pool is Pool.