That's a difficult question to answer. Take two identical boats with different motors and you'll get two different results.
It might be more meaningful to offer some comparative speeds -- at least the motor will be the same! At cruising speeds in still water, no wind or current with Turbofins, the i-12s is about 1 MPH slower than a Hobie Adventure and about .3 or .4 MPH faster than the I-9s. In sailing and paddling modes, the comparisons would be roughly similar. Obviously upwind hull exposure to wind and chop would favor the Adventure more and downwind the gap would likely shrink.
The i-12s has some excellent compensatory characteristics for it's lack of stellar speed -- excellent stability, huge load capacity and easy transportability. A friend takes his i-12s surfing -- something I would never try with the Adventure!
Hope that helps.