I've standardized my filters at 46mm because that is the largest diameter filter that I'd consider purchasing. I currently only have 50mm lenses (40mm, 43mm diameter Canons/Nikkors) and I just adapt to 46mm and use a generic shade because finding 40mm/43mm filters/correct shades can be tricky and pricey.

I'm thinking of purchasing some Leica lenses that are 39mm in diameter. The filters/shades are a bit more common so it is more practical for me to purchase the shades/filters. I do not use that many filters so it won't break the bank, but shades are expensive, and I'd rather consolidate accessories.

Is there any practical disadvantage for stepping up? I figured that the worse case is vignetting from the shade and viewfinder blockage.

I also figured that any deviation from the appropriate shade is a case-by-case so these are the lenses I'm interested in:
-35mm Summicron V1
-35mm Summaron
-50mm DR Summicron

Any experience with the generic heavystar shade and any advice on a not-too expensive Leica shade to cover these (incase heavystar isn't the best choice).