Go for the OVERDRIVE!
Unless you're trying to do the World Tour, I don't why anyone would want to sail full race sails with all the cams. The Overdrive is soooooo much easier to rig, feels lighter (it is lighter actually!), has the same top-end and control as the R4/5 and did I mention it's easier to rig?
Race sails are quicker to accelerate and have more power sailing at deep downwind angles which we need for the PWA, but most people wouldn't even notice. If I didn't race I'd never use a race sail again.
8.6m will definitely give you a big leg up for early planing and it's the perfect size for the 110. That being said once you're powered up >15 knots the 7.8m will be quicker for GPS runs ... But you already have the 7.8 SCR so why not go for an 8.6 Overdrive. You'll be suprised how long you can handle it in strong winds :-)
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