Here is a polar for a F18 in low wind conditions. It shows that the max speed is around 112º with the spi and around 75º without (A and B show the best VMG for the given wind conditions and are irrelevant for this exercise). The difference in speed between the two looks minuscule.

With a solo F16 (aka no jib upwind, less meat on the wire) I suspect the downwind speed is easier to achieve.

I should capture and use all those GPS tracks I have to make polars, as using someone else polars to extrapolate is not that rigorous scientifically

Also, so far my top speed have been attained while racing to a downwind mark, aiming for a good VMG, not a ridiculous speed. What this polar indicates is that I can probably go way faster if I'm not racing!