It all depends on how much you want to spend, as always! I can tell you that removing some weight and massaging some extra power will give you that "little 550", as you put it, you'll really enjoy playing around with! Here is a recipe that I found works great.
Make sure your engine bottom end is in great shape. How many miles are on the chains? (primary and cam) Better check the mains and rod bearings before you go too far.
Boring to use 61mm pistons is safe enough with stock sleeves and gives 592cc(either that 605 kit or standard 750 pistons-modified)
A good valve job and at least some porting (heavily modified ports will necessitate different carbs)
Aftermarket cam, even a mild street cam helps a great deal, aftermarket valve springs.
Tighten squish and increase CR some.
Different coils and ignition
Frame and suspension
All the usual improvements, check wheels & bearings, steering head attention, tight swingarm bushings, GOOD shocks, if stock forks interconnect and add some air, try progressive springs. Install good tires. Change the riding postion some if you lean to the sporting side of things. At least the things everybody can do easily.
If you can, remove weight too. Nearly twenty pounds alone with a change of exhaust, but start looking for a Kerker, It's been stated by better minds than me that the Mac won't give a power increase over stock pipes. Lots of other little tricks will remove heft.
It won't be race track competetive but you'll end up with a completely different middleweight that'll run away from your stock 750. (This might raise some hairs!)
