Is there any chance you could have a paddle in the SF S before buying it?
There's no doubt that the SF S is a bit less stable than the XT (I've just spent some time paddling the new XT S for a review that'll be posted in the next day or two), and it's a fine boat, but I find the SF significantly more responsive and satisfying to paddle.
I'd say, go for it. If you have the time to paddle it 3 x a week before the Gorge, I reckon that's ample time to get used to it.
For me the SF S is the ideal combination of performance and stability - I almost never have have to brace, even in hectic conditions but it also has near-elite capabilities in downwind conditions. At age 55 I'm still improving my Miller's Run time - breaking my personal best time three times in 2018... I just love the boat.
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...