Fastest I've recorded is 24.7 knots on a 10m Soul and and Moses 590/330 wing setup, but I'm not very fast (that was in maybe 15 knots of wind or so). Even that was a peak speed where my "fast" cruising speed is more like 20-21 knots. I'd love to be able to cruise along averaging 25+ knots, but I don't really know what to do to get there. I know I don't have the fastest gear out there, but it seems like it should still be doable.
Not to rain on anyone's parade but if you are using a basic GPS then they are highly subject to aberrations in speed readings. I see stupid numbers out of my Garmin Fenix every once in a while....where I know I didn't go that fast but I could certainly claim it. You really need a high frequency reading from something like a Locosys type device to have a very accurate reading.
That is why I use a filter to get rid of any outliers and spikes. I pretty much also ignore the 1 sec speeds. The 100m average is pretty accurate.
We have a nice flat water spot where there is shallow water on either side of a deep channel. I've had several ten second average speeds in the 34-35 mph range with Delta Hydrofoil and Sonic 2. 15m Sonic 2 in 14-15 knot winds and 11m Sonic 2 in 18-20 knot winds for top speeds. Top speed on Sonic 2's was 35.9 mph (31.2 kts, 57.8 kph). Upwind I was going ~22 mph when conditions were perfect.
Recently picked up a Sonic VMG 15m and it is way faster, but I get overpowered more easily. Second time out on it, I had a top speed of 37.6 mph (32.7 kts, 60.5 kph) in gusty ~18 knots of wind and choppy. I wasn't even trying to go fast, just surviving. Top 10 second average from that session was 34.0 mph. Upwind on the VMG I can stay at 23-24 mph at same or better angle than sonic 2 when conditions are perfect.