I've got a set of 06 Vanilla RLC's (same as R but with more adjustment) on my sub 5 which feel damn good. They were plush as hell straight out the box and are so light compared to other forks in this price bracket. I would recommend a set of them any day.
Id go for pikes... but thats because ive used them for a year and not had a single problem theyre stiff, reasonably light, strong and plush as anything. QR's a step down in strength and stiffness
i saw a guy rippin up the dowhills and doing the shed drop on a cannondale jekyll with a lefty fitted. So I guessin they can stand up to thatsort of ridin.
a set of 66's on the dudu would make it like a chopper. plus its a bit to much travel for what i do. only running 125mm out back so dont want much more than that up front
by sounds of things pikes would be cool, or some shermans, but as you said at start, leftys do have a certain appeal, so go for it(if youcan get the steerer conversion)