First just have to throw this out there, R3R vs Wing - Not even the same kind of bike, compare the Wing to a Trophy not a rocket, those are closer in class.
Assuming all is bone stock straight from the dealer lets look at some things:
Tires: Stock 880s are far stickier than the garbage that comes on harleys.
Brakes: Brakes, not even a contest, extra weight be ****ed, the Rocket stops with an insane amount of force. Money that a single front disc XL1200 with more rear weight bias and much worse suspenders would add a huge amount to the R3R stopping distance.
Weight: XL1200 - 553 dry, Dyna 650 dry, R3R 704 dry.
Suspension: The base XL1200 and R3R have only rear pre-load adjustment, so that at least is even.
In the real world it will all come down to the rider, as usual. Same pilot, familiar with both bikes on a timed course, rocket is going to win every.. single.. time.
My anecdotal evidence

:
Considering I leave most of the locals with hopped up Thruxtons for dead around corners (straights they don't even try), I
seriously doubt a XL1200 will put up a fight with anything less than well versed track rider in command. On the same note though, I usually leave the jap 1000 riders for dead on twisties on my Daytona 955, a "fat and slow" sports bike....
The real problem in comparing any HD to anything else even remotely sporty, is the vast majority of HD riders I know, have no desire to go corner fast, usually its 10-15 mph over the posted limit and that is fast for them. They are 40-60 hp bikes, sold on an image, to people looking to have a certain image. It doesn't lend itself to finding many who can or want to actually ride hard.
Start talking modified bikes, then I would hand the win to the XL1200 however. They have pretty much the entire list of mod parts available from mild bolt on, to wild 9 second drag bike, to flat track setups, to road racing setups etc at their disposal.