nit: there is no Linux "v6" or "v7". The first and second version component cannot be separated, it's v6.0 and v7.0. Versions 6.0 and 6.1 have as much in common as 6.19 and 7.0. You could also call them 3.60 and 3.80, or 2.6.100 and 2.6.120.