Maximum sink size for 600mm unit

Hi all

I'm wondering if anyone know what the minimum space should be between edge of sink and edge of base unit for undermount fitting. I am trying to figure out what the biggest sink size I can get to fit into a 600mm IKEA unit.

I saw a sink I quite like and it's 550mm wide, website says it's for 600mm cabinet but didn't clarify if that's an inset or undermount fitting.

Also, I am buying a sink from a private seller on eBay (he bought the wrong size). Should I be worried about sink...

Maximum sink size for 600mm unit