Thinner means you won't be leading on it unless you're going with double/twin ropes. There's not much in the sub 9 mm range yet and it really is for limited applications, you're not going to work your sport project on an 8.7 mm rope (unless your pockets are way deep). I use a 9.1 or 9.2 when I have to walk far (using one of the BD ropes lately) and a cheap 9.8 when the crag is close or I know there will be lots of top-ropes or other shenanigans.
As far as the Petzl RAD system goes, it's not really climbing-oriented and 30 m is a deal breaker. I have a dedicated 8 mm static rope I bought years ago to use for rappelling on long routes only but it's a PITA to trail. IMO you'd be better of with a dedicated 6 or 7 mm rappel/pull cord carried in a pack to supplement the lead rope. Seems to be the most common system you see in places with long ass routes like Red Rock.
Regular single rope + 6 or 7 mm pull line
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