I've tried both, including Rickman Honda 750 and Rickman Kawaski 1000 (bore kit, before 1000 was out). Kawasaki is wider than Honda and needs alternator cover modified before you break it. The frame mod for Kawasaki isnt too difficult and improves thing so much you wouldnt believe the difference. The Kawasaki is much faster to get to top speed, the weight isnt noticable higher than CB750. When modded it flexes less than moddecd CB750. Sorry to burst your bubble
Here's a pic of my sisters bike, just before she sold it (about 2 yrs ago-2004) Tank, side panels and tail unit were restored to original paint, didnt get round to rest of it. It's been in the family since1978, we dont sell stuff too often.
PJ