The Schneider website gives recommended coverage for their lenses, see the PDF. Schneide use th continental formats but the figures are fine for the UK/US equivalents.

I know that my 210 Rodgaon (Rodenstock) doesn't quite cover 10x8, it vignettes the corners but a 240mm Componon (or S) is recommended, I've used a 135mm Componon for years for 5x4, again recommended bySchneider.