OK, @Carlos P, Here's my 2 cents worth.
I have a full IRS (non-swing arm) car with 205/16" wheels all around.
All four wheels are original Fuchs (not reproductions) from a 911 (now all 6" wide) and the tires are Michelin something or other running tire pressures of 22 front, 26 rear (yes, they are a tad stiff - I could probably drop a pound or two).
I have had all four wheels/tires "Road Force Balanced" to perfectly dial them in. It took me almost 20 years to discover this service and get it done and I wonder each time I take her out why it took me so long - It's that good.
I have had a 4-wheel alignment done (1970 VW sedan specs) where the front end caster was set to 6º . THAT was very important because before that, she wandered, chasing the crest of the lane and any bumps she found. That made the front end seem squirrely and it wandered a lot, especially with cross-winds. After a proper alignment and getting the caster between 5º - 7º, she became very stable above 60mph and stays that way all the way up to 100 or so (on the track, of course ). It is sometimes still a bit subject to cross winds, but it's a pretty light car so I can live with that and it's minor, to be sure.
I have run a combination of tires of 205/16 front and up to 225 rear (I have a wide body car) and after a proper alignment and caster adjustment I see no highway difference between the larger tires and going down to 205s - It seems to handle similarly on highways with either, but the 225's on the rear REALLY made a positive difference cornering hard on the track.
So, to summarize; I feel safe and secure at any reasonable highway speed up to and beyond 85-ish, including riding in the turbulent wake behind a tractor-trailer, given setting my 4-wheel alignment to the 1970 VW sedan specs but adding caster to get to the 5º - 7º range. THAT made all the difference.