Some additional thoughts on lens choice . . .
A viable option with the R3A would be a used 40/2 Summicron-C or a used 40/2 M-Rokkor.
The Voigtlander 40/1.4 has received a lot of attention & discussion since it was announced 3 months ago, it has only been sold in japan so far & is just coming on the market in the rest of the world. As such, very little is known right now about the quality of this lens, so it might be better to wait until more is known about it. Regardless, I think there are better choices to use on a Leica M6.
The VC 35/2.5 is cheap & compact. If you are referring to "Classic" version, you will need to factor into the cost an extra $50 for the cost of an adapter. The 35/2.5 P II (pancake version) is made in M-mount, so there are no additional costs.
The current Leica 35 Summicron-ASPH is by all accounts an exceptional lens, far better than any previous 35mm lens. Many people, however, love the previous non-aspherical version, referring to it as "the king of bokeh." Interestingly, Leica expert, Erwin Puts, sees little difference between the Voigtlander 35/1.7 Ultron and the non-aspherical Leica 35/2 Summicron. Although he gives a slight edge to the Summicron, I'm not sure if you or I would see the difference depending on the type of pictures you're taking. If you do notice a difference, it would probably be in the quality of the out-of-focus background in the picture (bokeh). How important is this to you? For my money, the VC 35/1.7 on either a Bessa R2, Bessa R2A, or Leica M6 would be a viable set-up.
To confuse matters even further, refer to the link below for the opinion of photography writer, Mike Johnston, in yesterday's column: "The Best Lens for a Leica."
www.luminous-landscape.com/columns/sm-dec-04.shtml
(PS - His choice is any version of the 35 Summicron, but the kicker is that he likes the bodies even better than the lenses.)