Sorry for the delayed reply.
Firstly, to clarify, the "Jekyll and Hyde" comment was made to try and describe a potentially positive nature/charceter in the iS101, it should not be interpreted as a critisism of the 101 (quite the opposite).
These days there's also emerging trends within slalom to differentiate board selection/choice for more (pure) speed (GPSSS) performance focus vs allround, versatile on water slalom performance - and this differentiation can easily result in two different board choices for otherwise identical riders in identical conditions.
For me the 101 is incredibly verstatile open water slalom board, "large" enough (on water to have the ability to carry moderately large sails (up to about 8+m for 90-95kg) but still small enough to be super fast in the more powered (6-6.5m) open water conditions. Typically that was the domain of 2 boards - now comfortably nailed in one (with 2 characters, Jekyll and Hyde).
However, in the same conditions for GPSSS use, where top end rules and everything is a distant second (including otherwise important aspects like range, upwind etc) the better choice has proven to be the iS96 (and this is why you may have the impression I would favor it over 101). Of course in GPSSS (and related) style sailing, the board is also often sailed with less sail area (for top end tuning) than what you may use in open water racing - so selecting a board with extra width and sail/fin potential for verstatility sake is not so desireable if top speed is the main game.
In typical open water 6.2m and 6.7m conditions, a 70 kg experienced rider should be fully within the range of the iS96, especially if you disregard larger sail/fin (lighter wind) potential of the iS101, however as you have found from the 2007 101, even if you don't max out the sail/fin size, that extra width on the 101 really adds to the ability thru lulls and (maybe critically in offshore condition) upwind.
If you're figuring on adding a higher wind board also into the quiver (ie : Futura93) then that is also a solid reason to take iS101 (rather than iS96) as the range overlap FU93 to iS96 would be on the excessive side of practical.
Depending on the methods used, the absolute volume measurements can vary (slightly).
However, using the same method the relative displaced volumes for 2008 are iS101 (96 lts) / iS96 (96Lts) and for reference FU93 (94Lts). anyone familiar with iS101 vs iS96 will be well aware that the 101 definitely rides "one size" bigger than iS96.
Hope this helps resolve the questions, please let us know if you need more info.
Cheers ~ Ian