In the end, this is Spain and everyone goes as fast as they please until they either crash or see a cop car.
That's what I did when in Spain: I quit flooring it at 150 km/h, and I was only passing about half the traffic at that speed.
America went to 55mph for virtually all highways in 1974, it was raised to 65mph (at an individual state's discretion) in 1987 (I remember reading the newspaper article in 7th-grade current events that day...never mind I couldn't drive yet), and finally each state could pick its maximum limits around late-1996.
Florida jumped to 65mph for most limited-access highways (interstates and toll roads) and a few stretches of open-road, 4-lane dual thoroughfares by 1987, and finally in early 1997, the state maximized highways to 70mph, open 4-lane highways to 65, and two-lane road maximums were now 60mph, where they pretty much are to this day.
Mind you, most speed limits where I live, in the urban and suburban areas, has actually dropped in a lot of locations, even after adding more and wider lanes, longer turn pockets, and smoother surfaces. The increase in traffic lights and overall density of traffic has burdened some roadways to the point where signs aren't really needed; all you're going to do is stay at that speed for about 30 seconds or so until you have to brake or stop again.
What is more annoying is when the speed limit bobs up and down every mile or two. For example, on one 10-mile stretch of 4-lane roadway I use frequently: 45 - 40 - 45 - 40 - 35 - 45 - 35...Just annoying.
Simply put, make it 50 around the suburbs, 35 in gridlocked situations, 25 in residential neighborhoods, 20 in school zones, and 90 mph on left-lanes of the highways; 75-65 on all the rest: Save tax money on all the unnecessary signs and stop making us panic over victimless crimes.
South Florida has terrible driving ethics compared to he rest of the state: Pass where ever you like, signals mean nothing, make a left turn into whatever lane you want, make right turns on red without stopping, hold up every one else because you're too chicken to even follow the laws, make a left turn 3 seconds after the light turns red, stay in the left-lane at 10mph under the limit with you blinker on for two miles...patience is the key, or you'll go mad. I stopped cursing at the others over 10 years ago, you live longer.