A better comparison is the Stockholm C – Uppsala C SJ-operated non-stop services, which like the Miami to Ft Lauredale services take exactly 30 minutes.
This is 63 km (39 mi) as the crow flies (66 km by track), so an average speed of 126 km/h (78 mph), substantially quicker than the Miami to Ft Lauredale service.
Taking a look at Google maps that is not really comparable either. Much of the area between them appears to be rural with a low population density where as Miami to Ft Lauderdale is high population density the entire route. Train speeds are limited in high density areas for safety.
> Train speeds are limited in high density areas for safety.
There are plenty of places in Europe where 100mph+ running through urban areas is common. Urban v. rural isn't really a consideration for line speeds here. Heck, most of the mainlines north and west out of London reach their 125mph top speeds while still within Greater London. The question here is more about the presence and type of at-grade crossings, and there's a fair number on lines with 125mph running.
This is 63 km (39 mi) as the crow flies (66 km by track), so an average speed of 126 km/h (78 mph), substantially quicker than the Miami to Ft Lauredale service.