I'm thinking of aiming for this next year, not sure about my bike though. Kona Dew hybrid with trekking bars, list weight about 13kg, 700x28 Conti Gatorskin tyres, 28/38/48 front ring with a 11-34 Megarange on the back (next gear up from the 34 is a 26). It's not slow, but it's not zippy, especially up the hills which could make all the difference on this route. I would probably switch the Gators for GP 4 Seasons as I never quite trust them on fast/wet corners.
I got round Arran in 4.5 hours, about 25 minutes of that was resting, and with 5kg of kit and water in a pannier which I likely wouldn't need to carry. So looking to come in under 9 hours - what's the cut off time for the 3 Pistes?