That's correct Cat6 maxes out at 10Gb on short runs. It's also a case that there's an issue with heat, trying to push 10Gb over wire - usually exhibited in the SFP+ transceivers, switches and such, which is reduced with 6A and better.
In 10 years time, will you wish you had made the minimal additional investment in 6A over 6 when speeds increase and your wires are all behind sheetrock or plaster? I've already done multiple build-outs in commercial and homes, and I'm well aware of how quickly these wiring jobs become obsolete. So I won't even touch anything below Cat6A today.
Addendum: the heat issue that causes 10Gb copper wire SFP+ transceivers to burn out is why I'm running fiber - significantly cheaper running costs too.