Well a good mate of mine actually had the ST93, and I have sailed it a few times. He thought it was fantastic for lake sailing (chop etc), using a 6.5 NP V8. Infact we lined up the ST93 & F93, and rode both with 6.7 RSR. We concluded that the F93 planned a little earlier and went upwind better. Top end speed was neglible, and thought more came down to rider input.
When it comes down to a choice between the F93 ST93 and I86, for me its the I86. However I sail mainly flat water with moderate chop. If it was really heavy chop, I'm not sure in 5m weather, whether any of these would be much fun, I'd prefer to be on an acid, chop hoping etc. For me the I86 going off the wind in flatish water, or cranking a gybe on the end of a 30+ knot run is the go.
I have on order an I122 and a I101. I'm picking the 6.7RSR and I101 will be a sweet combo in 15-22 knots. I find although the I86 gets going in 15, its not until around 18/20 it starts to motor, I'm 87 kg by the way....