550F is my favorite four, including the Rickman CB750 which was quicker accelerating but about same top end (130 ish' mph).
I worked at a Honda dealers and got to ride all of the fours up to the dohc 750/900's
Modified 550 is lighter, just as quick as a stock 750 but with better handling (less weight, narrower engine, etc)
I owned CB550F1, 550F2 and 550FourK at the same time for comparison
400f's are OK but have major variations in handling, some are great, some try to kill you
I also had a CB500f for a very short time, seemed a lot lower than 550 for some reason (springs probably worn out?)
It also seemed smoother running than any of the 550's?