According to my 5 second google search, the "most common" speed limit (inside urban areas) is around 50 mph (80 km/h), meaning Caesar drove at 250 mph (402 km/h).

Also according to my 5 seconds google search, a Harley Davidson, a popular IRL bike I chose because that's the first one that came to mind, can reach the speed of 115/120 mph, up to a "maximum" of 160, meaning that Caesar's bike is tuned as fuck.