I'd definitely rather have a 5x7 or 8x10 than a 4x5, but film availability for 5x7 seems...limited. I only know of ten film stocks available in a 5x7 format[1] vs. 25 for 4x5[2] (including some C-41 and E-6) and 19 for 8x10[3] (again including C-41 and E-6).
And then, of course, 4x5 seems moderately impractical, and 8x10 only more so ;)
There is more 5x7 than that - Fuji still make some http://www.japanexposures.com/shop/film-analog/film/sheet-fi... and Kodak Portra is available for special order, and thats just the colour ones. You used to get a bunch in half plate and European metric sizes too, although less now. (I also have an 8x8 back for my camera and cut down 8x10...)
And then, of course, 4x5 seems moderately impractical, and 8x10 only more so ;)
[1] http://www.ishootfilm.org/film?utf8=✓&film_size%5B%5D=size_5...
[2] http://www.ishootfilm.org/film?film_size%5B%5D=size_4x5&utf8...
[3] http://www.ishootfilm.org/film?utf8=✓&film_size%5B%5D=size_8...