do a quick calculation for the total displacement increase. i'm sure the oversizes are only .25 or .50 mm each jump, so displacement can't be a huge increase. For example:
Stock CB750 stroke is 63mm and stock bore is 61mm. this gives a volume of each cylinder of 184cc, so 736 total.
Increasing to the CB750's 2nd oversize piston (.5 mm) yields a displacement of 748cc.
Increasing to the 4th oversize (1 mm, which I did) yields 760cc.
As you can see, not much of a displacement (or power) increase. I combined my 4th over kit (wanted it to be "stock") with a 0.010" decking on the cylinder head and a more aggressive cam. Generally, if you increase the volume of fuel/air, you will benefit from an easier path for it to follow (headwork and cam).
To answer your question: doing just the overbore is what you should do if a good hone still leaves too much gap between piston and cylinder wall. Honda believed in their bike by offering 4 sets of oversized pistons. Add to that the 812, 836 and so on and you could potentially have a CB750 that lasted dang near FOREVER!
So unless you have clearance issues, i would just do a good hone on the cylinders and it's doubtful you'll feel any big difference from an overbore w/o other performance work to compliment it. Hope this helps!
