Timbo/Scooby,
It has been my experience when there is a " B " mark to just round " A " and keep on going as it is normally too high to run the spinnaker even with the traveler all the way to the stop!
As far as the main's telltales, I keep them flowing also with adjustments in Mainsheet tension and traveler adjustment. The more twist you have in the main the faster downwind. Remember, I only cleat the spinnaker on distance races and then only when you are sailing relatively close to the wind on the downwind angle. While buoy racing, you must constantly work the spin sheet unless you get a good lead. Then you can cleat and rest your arm.........same if you are way behind. The F17 has a way of totally exhausting a person of almost any age especially during an afternoon of 16 - 18 knot buoy racing. When we raced last weekend, the conditions were near that, and I was exhausted after 4 races being out of sailing shape and all.
I am running 4 ratchamatic blocks without the attached cleat..........
Tom