Well im sure Martin wouldnt say it unless it was correct about the valve size, but bare in mind that if you are only after moderate gains (like 250bhp or something) then bigger valves would only make it more laggy and shitty low down and given no gains up the top, bigger isnt always better when it comes to valve size.
Obviously if you are tuning the absolute nads off it though, you want to be starting with the biggest valves available in any of the standard cars for that