I think i just need to get a few....Maybe in the 130-150 range...I think after handling one, i would mind having a few in my kitchen, and maybe for future offerings. Not sure but i think a 140-150 is a standard 240 gyuto size? Not sure.....I have a 135 petty i made with a 130 handle on it...I like it quite well, but not sure if there is a standard....?
I can't see any standard, huge differences between makers. But that's the fun of custom work, you can do whatever you and the customer agree on. I have my own personal rules of thumb, but there is quite a bit of flexibility. I find the really small knives to be the most difficult to match a handle to, around 145mm for a 240 and maybe a little longer for a 270 sounds about right in most cases.