after thinking about it, here's my thoughts. i'd like to hear some other thoughts toward it.
theoretical:
1. all that matters is getting from point A to point B within a certain time period. since notes must be clicked within a specific time frame the only thing we worry about is discovering where point A and B is. in this game it's the approach rate. notable approach rates are 300, 400, and 450ms.
http://puu.sh/ZHaC0If larger area is easier to get better accuracy, then the best tablet area is the largest area at which one can move from the farthest point A to the farthest point B within the time period of: (300ms - your reaction time)
realistically:
1. getting from point A to B is not time-precise every time: if you need to react with 50ms, you can't react/read 50ms jumps every time. therefore, the "perfect tablet area" should be slightly smaller to allow time for more reaction.
2. you can not move your hand so-perfect-precise
fast every time. if you expect to do that, then you should also expect to be able to to do perfect-precise moments in a small tablet area hitting every note.
what this means is either you'd have to lower the "perfect tablet area" even more, or adapt with it and have less time to move from point a to point b. or in other words, full area vs not-full area.
my conclusion:
1. If you aim to be the best game-play wise, then I believe a small/medium area is better
2. if you aim for high rankings and still be a very good top player, then I believe a full area is better.