Hi Wouter

you said:
-1- First is trivial, If both are sailing without a spi then the sloop is definately faster around the course.

my opionin:
If this would be the case, all the A-Cats would carry a gib....

you said:
-2- The unirig has the same overall sailarea as the main+jib combined of the sloop and both sailing with spis. With the right mast height (not too high) the uni will sail just as fast or slightly faster upwind than a sloop rig. While reaching the roles are reversed.

my opinion is
When sailing under gennacker, the gib IMO dosn't do mutch.
I think the Uni will be faster, because with the higher mast, you can hoist a gennacker that has a better aspect ratio, there is a bit more wind high up and I think that the high aspect main will be more effectiv too.