>although for cards that are backed by a credit card, I think the limit is higher

I have a Suica thats integrated into a credit card, and it still has a ¥20,000 limit - the Suica balance is separate from the card balance, it just has a configurable auto top-up setting.

Interestingly, if I'm out of the Suica zone, sometimes auto top-up won't trigger. If I recall correctly this happened to me once in Fukuoka, presumably because there's some level of integration above just accepting payments that Hayakaken hasn't achieved. Never had a problem with Passmo interop though.

I've never heard of a suica with a higher limit, but it's possible they exist or that other compatible cards have higher limits.