At 6'2"/1.87m/85kg I couldn't fit in the G20 and found it very tippy. As you've noted, it's designed for smaller people.
The G40 was a lot easier to paddle, but I'd agree with jagter that it's possibly a little more tippy than the V10 (especially the new one) in terms of stability. The seat is very different though, a lot narrower, more like a Fenn bucket, and a lot deeper; the G40 has quite high rails.
It doesn't have much rocker as I recall. In the kind of short, steep wind generated downwind conditions that we get here in Cape Town, I found that with the standard rudder at the time (2+ years ago) I found myself broaching if I wasn't concentrating... A bigger elliptical surf rudder would probably go some way to sort this out.
There aren't that many of them around here, but at least one elite level paddler was doing well on one.
I spent a lot of time on the Genius BLU and liked it - particularly in big downwind conditions. I found it very responsive, easy to get going on the runs. I had a big elliptical surf rudder on it.
Rob
Currently Epic V10 Elite, Epic V10 Double.
Previously: Swordfish S, Evo II, Carbonology Zest, Fenn Swordfish, Epic V10, Fenn Elite, Red7 Surf70 Pro, Epic V10 Sport, Genius Blu, Kayak Centre Zeplin, Fenn Mako6, Custom Kayaks ICON, Brian's Kayaks Molokai, Brian's Kayaks Wedge and several others...