Looking at my Toggl, I've logged ~35 hours/week over the past few years since becoming self-employed.
However, I log hours for meetings and work travel (and personal stuff like volunteering and online courses), which tend to require less concentration. When I subtract those out it's more like ~25 hours/week of "deep" work.
I only log the hours I work, so it's hard to tell how much of my remaining time counts as a break. But I doubt I'd be more productive at a 40 hours/week job, so call it (~25/40 =) 62.5%.