All the multis have a "slow" gearchange due to the design of the selector drum and forks.
Having built both the Honda CB 500/550 and Benelli engines, they are remarkably similar and the Benellis are an obvious copy excepting slight differences in manufacturing tolerences and sizing. Therefore while internal parts are not all directly interchangeable, many Honda parts can be fitted with modification. My own Sei special runs Yoshimura CB 550 pistons, valves and guides and a Ravasio cam with modded rockers to clear the "wild" cam lobes.
The Benelli valves are however slimmer for gasflow and on paper should give more power, but that's not always the case if the engine explodes!
The gearbox issue particularly with worn engines is often largely down to the selector drum tensioner arm sprung scissors design - Look in the parts book to see what I'm talking about.
The Honda one comprises 2 pressed steel rivetted washer rollers, all very cheap and nasty.
The Benelli one has been "improved" to a design with a bombproof roller bearing on one side, but due to space constraints retains a rivetted washer on the other arm. Obviously, this rivetted part now suffers ALL the wear and as a result the rivetted spindle tends to go oval VERY quickly with hard use. This has the effect of leaving the drum under tensioned in rotation and you can get stuck "between gears". This causes missed gears and in the extreme, possible selector fork/gear dog damage especially if you have a heavy boot.
Theferore when re-building, pay attention to this element and replace the rivetted part regardless of any wear.
These bikes will never we as slick as a modern machine, but then again neither are the CB Hondas of the period. Don't expect Suzuki GS bulletproof gearbox performance from these engines and don't get paranoid and you won't be dissapointed.
I hope this helps more than hinders!