I would say that 1 pt of intelligence is about 10 IQ points.
IQ 100 is average and 173 is IQ that is less thatn 1 in a 1000 people have.
And there was only a handful of people with IQ200 and above in history.
I've always played that a +1 modifier represents one standard deviation above the norm. Since a "genius" is someone with an I.Q. of 145 or higher, this would exactly be an INT 16 or higher. While this translates into a narrower range (max I.Q. would be 175 with a +5 modifier), the number of individuals with an I.Q. higher than that really isn't very great and it gets to a point where being smarter doesn't really have much impact in practical knowledge use or theoretical capability. In general, any one with an ability score (in any ability) of 14 or higher is able to do or learn whatever they need given enough dedication and practice. An INT 8 with a -1 modifier would be an I.Q. 85. Such a person is still intelligent and just as capable, but might be forgetful, have trouble concentrating, or take longer to learn new things, etc.
When we think of strength, someone who is a professional athlete or works an
extremely demanding physical job would like have STR 16 or higher, with the very strongest reaching STR 20. Your person who works out regularly and does occasional physical activities (hiking, biking, sports, etc.) would likely have a STR 12, maybe 14. Now, that doesn't mean they
have to, of course. Someone with a STR 10 could just as likely do the same, but since ability scores represent such things... it sort of follows IMO.
Some people aren't comfortable quantifying people in such a way, but it works for understanding how ability scores might translate IRL as far as I am concerned. I explain it to new players that way and they get it.