In town, pretty darn slow. Too many unpredicatable pedestrians, cyclists, joggers, etc.
On the highway I try to be faster than about 90% of the traffic while still getting passed by the other 10%, whatever that speed is. This way I can usually exceed the posted speed limit and not get ticketed.
On the way to work that usually translates into 70-80 mph during ideal conditions. One drop of rain, however, and it can drop below 55 mph.
On long trips on the interstate in downstate Illinois, in my extensive experience, 75-80 mph will generally not grab the attention of the state constabulatory unless you are driving a Porsche or Corvette in which case 64 mph in the slow lane is recommended.
The riskiest of all is when no one else is out and you cannot hide. Despite my never having used a radar detector, I’ve been pretty lucky. I can’t say how many times I’ve maintained speeds of 100-130 mph over great distances and yet was never ticketed.
I’m out of that game now, though. In Illinois if you are ticketed for a speed in excess of 100 mph they take you straight to jail where you will languish until you see the judge the next weekday morning. The fine is a minimum of $500, the ticket is on your “permanent record” and your license will be suspended, guaranteed. Auto insurance becomes pricey. FYI.
There are just so many variables that a fixed speed limit cannot account for that I feel most highway speed limits are almost irrelevant. What if it’s dark? What if it’s raining or snowing? Fog? Deer crossing? Hellacious traffic? New Year’s Eve?
What about perfectly straight highway for miles, ideal driving conditions and no one on the road but me? Montana had no fixed speed limit until recently, just “reasonable and prudent.” Porsche on a straight empty stretch at 150 mph = no problem. But wouldn’t you know it, someone had to challenge “reasonable and prudent” in court as too vague. Everyone lost and now Montana has a fixed speed limit.