measured with gps, max speed is 161kph with my totally stock 76 550F. it occasionally goes up higher but it seems like it's recorded as max speed only if held for a minute or so.
cruising with regular highway speeds (in europe) around 120, 130kph for hours is no problem.
reliability - depends on how you treat it. if you maintain it well (following the manual), only mistreat it occasionally and don't do anything too stupid (like running it beyond redline all the time), these engines will serve you a very long time.