I've been doing a bunch of gel experiments lately, and I want to get my conclusions down before I forget them.
Whipped Gelatin foam: for powdered, 1% seems like a good concentration, though the resulting gel is quite fragile. About 2 or 2.5 sheets (gold I think) for a quart of sorbet base did well at work - much stiffer than the 1% powdered, but the mouthfeel was excellent. Whipping when the gel is more firmly gelled seemed to give larger bubbles and a more aggressive bubbly mouthfeel. Almost carbonated-seeming at times.
Agar: .5% worked well for a soft gel that melts quickly in the mouth. I had to add water to readjust the concentration before chilling because so much water evaporated during the hydration and dissolution process. Made a fluid gel around 1%. No structure without added starch, felt almost like water on the palate. A higher concentration lasted too long in the mouth in an unattractive way. A little added starch (Ultratex 8) gave an ok sauce-like mouthfeel and slightly more structure on the plate, but might change flavor release at a higher concentration.