You want the appropriate length cable (inner & outer) for your handlebar height.
What Bob said is mostly right. All of the different length cables will (should) have the same cable-to-sheath ratio.
The free-play in all of the cable assemblies should be the same, because you want the same clutch adjustability, regardless of handlebar height/clutch cable length.
With the low bars like you have, you would want one of the shorter cables, so there is not a lot of slack hanging around - which usually would be down by the lower R-H side of the engine/frame, at the front.
Too short, and you would not have enough free-play in the sheath, causing binding when the handlebars are at full lock, one way or the other.
I think the only clutch cable that would be too short would be the one for the R100RS (L=1386MM), with it's very low, narrow handlebars.
R100RT - L=1520MM
R65 low bars (European models) - L=1386MM - Whoops! Same as the RS!
R65 high bars (US models) - L=1495MM - shorter than the RT.
I got all of these figures from RealOEM.
