[Nyororin]

I am a girl, and I have dated American and Japanese men... And am married to a Japanese guy.

I have found that there is really no difference - at least not between white American men and Japanese guys.
Well, white guys tend to be bigger while flaccid.

Condom sizes have a lot more to do with the "condom culture" - if you can call it that. Japan teaches that condoms need to be TIGHT - "use the absolute smallest you can fit into". America tends to lean toward "use the most comfortable, as long as it doesn`t slip off".
I think that this MAY have something to do with the harder / softer thing, but can`t really be for certain. Something in a very tight condom is going to feel harder than something in a larger one.