The answer here seems pretty obvious. The larger neg will enlarge to a much larger size until it shows grain. If you're printing both the 35mm and 6x7 to the same print size the 6x7 will always look smoother and even slightly less sharp simply because it's a larger negative. Until you get to a larger print size. Enlarge both negatives to 20 x 24 and let us know what you think then. I bet you'll like the 6x7 neg better. Grain isn't always a bad thing. There is a sweet spot with a particular print size for each format where the grain gives just enough feel to promote sharpness. In 35mm it's around 5x7 or 6x9. If you enlarge your 6x7 negs to this size there won't be as much grain and they can appear soft. All that said I have no doubt the Leica glass is sharper than the sekor lenses.