How about this potential scenario (totally need to check my trigonometry on this):

- light air limiting boat to hull speed upwind/down (without spin)
- 1 NM w/l course
- 30 TWA up
- 180 TWA (DDW) down with no spin
- 120 TWA with spin

So the two boats sail:

NO SPIN boat
Distance sailed = 2.366 NM
Upwind speed = 5.36 kts (hull speed)
Downwind speed = 5.36 kts (hull speed)

Time upwind = 15.29 min (1.366 NM zig-zag)
Time downwind = 11.19 min (1 NM strainght downwind)
Time on course = 26.48 minutes

SPIN BOAT
Distance sailed = 2.73 NM (because you're not sailing DDW)
Upwind speed (reduced jib area) = 4 kts (25% reduction in speed)
Downwind speed = 7 kts (30% increase in speed)

Time upwind = 20.49 minutes (1.366 NM zig-zag)
Time downwind = 11.71 minutes (1.366 NM zig-zag)
Time on course = 32.2 minutes


Furthermore (also suspect to math error):

To match the non-spin boat's 26.48 minutes on the course, the spin boat (sailing the longer downwind course and having a slower upwind speed) would have to sail almost 13.5 kts speed downwind to catch the non-spin boat.

So if cutting the jib down drops the upwind speed by 25%, the spin has to almost triple the downwind speed (from hull speed) to sail the longer course in the same time as the non-spin boat...