When I had 6/4 distance vision the maximum I could see a light aircraft was at about 3nm, a Hawk sized aircraft at about 5nm and a tanker at about 10nm. That was using an air to air RADAR to que my vision and get an accurate range.
These days I am 6/5 on a good day and 6/6 on a bad day as I approach my 55th birthday and I need readers for n6 close in work. So my eyes are definitely worse. So I can probably knock 20-25% off of those distances now.
Which is also why I believe that EC for GA outside of about 8nm for air-to-air detection is pretty pointless. I try to think of my aircraft flying in an 8nm bubble and +/- 6,000ft. Outside of 8nm then I am highly likely to see it as it will be chuffing HUGE, and inside that if I haven’t spotted it then I want to know about it. Anything outside of that is just an unwanted annoyance in my personal opinion and likely to distract me unnecessarily.