Average 40 knots is really, really, really a lot of wind. Open water sailing in average 60 knots sounds rather absurd: it is Force 11 on a Beaufort (heavy damage to trees) and I doubt any small vessel can sail in those conditions and survive.
Max gust speed means almost nothing, and if anything it is much better to go by sail size, and forget about reporting pseudo-exact numbers that mean very little and are always biased upward. For an expert level sailor 70-80Kg: if you are on a 4.5 you are probably not in a lot of wind, if you are having a hard time with a 3.2 something is blowing hard.
So, I am not sure any longer what are we taking about, but your numbers seem very biased upward: sailors in the Bay Area (either kiters or windsurfer) are very used to high wind but when it is blowing 4.2->3.7->3.2 you see proportionally way more windsurfers out in the water.
BTW: up to a certain point the main limiting factor for board speed is not so much the wind, but, everything else being equal, water conditions. That is probably why your (slow) GPS speeds decrease with wind speed. My top speed (2 secs) is 38.3 knots, achieved in nothing special: just very powered up conditions with a 6.0 and water that was exceptionally smooth due to a lucky combination of wind/tide. In regular conditions at my local spot I cannot cross the 33-35 barrier no matter what I do: too much chop.
Speed records, by the way, are back in the hands of sailboats, and they are there to stay. The only reason Kites held the world record for a little while was because they can sail in 4" of water (basically on the beach, in ultra-smooth water). But both kites and windsurfs are limited by design to very low efficiency: above a certain speed they go barely faster than the wind. Compare to www.hydroptere.com
the current record holder which did 51.36 over 500m and a completely untouchable (for kites/windsurfers) 50.36 over a nautical mile, in around 25-30 knots of wind ... in open water!