It’s enough to push my current fitness but without killing me.
60, 80 doesn’t really matter
So basically more junk miles. I reckon you’re overthinking it. If you want to ‘push your current fitness’ then the chances are you need more intensity rather than more volume, which you have a fair bit of already. Why not extend your long ride and look at doing some more structured, intense stuff the rest of the time.
Go out and ride jagged hills hard a couple of times a week for example. Build in some sprint efforts on flat sections etc. The rest is basic fuelling and recovery stuff and it’s hard to generalise as everyone works differently depending on age and physiology, but probably don’t do hard (intense) days back to back etc.
If you just want to ride more then ride more, but if you want to get faster/fitter, you should maybe look at a more structured approach and build some intensity in rather than just volume. That’s my take anyway.