I have the original oval Rapid Aero bars with the 480 foot pack and the bars measure about 50" with the end cap so I assume it is a LB47. I have only about one inch of overhang past the foot pack.
Go with whatever Thule recommends and you can always cut the bars down.
Thule new fit guide for the A3 is kind of confusing. Looks like there is a different rack and bar length for Open Sky or normal roof. (I have Open Sky)
That new AeroBlade bar looks nice. I was concidering the Whisbar but went with Thule. Wish I new they had this coming.