Depends. Common 4-lane setup tends to flow like130, 120, 100, 90, with trucks not allowed to leave the two slower lanes or exceed 100/110.

Also depends on the country, but people generally stick to the 130 limits with a few speeders pushing 140/150. Unrestricted zones still have speed limits to lanes so only the fastest lane is unlimited. Some countries the speed signs are just ignored because they're ridiculous. If you were to adhere to them, you'd put yourself at risk with the rest of the flow of traffic.

I'd say most of the time, cruising easy, and in usual traffic you're between 110-130. So 120 avg. or 75 mph is about right.