I think the Voigtlander line is quite capable and a very nice bargain. I've recently acquired a 21mm f/4 and really like how it handles. I went the more expensive route when building up my Leica kit, but doing it all over again - an M6 with Voigtlander lenses is a great option that would have saved me a lot of money. There is nothing that compares to the 50mm Summilux ASPH in my book, but for almost the same capability and nearly 1/10th of the cost, you can still take great pictures with the Voigtlander line. If you are patient thought you can pickup a Zeiss ZM Planar f/2 for less than US$700 and it is a wonderful lens as well.
Enjoy the M6 and post some photos when you can!