without having an idea of budget, and you've cast the net fairly wide, and depending on what era you like, I will add my comments to the "get an SOHC4" post above. Ive got a CB400F and I really like it. not everyones cup of tea, but a very well regarded thing in its day. Handles OK (again, for its day) but the big difference between an old bike and a new bike is brakes, followed by tyres, followed by ability to go round a turn. I think its called "handling" and the Japs didnt really get that till the mid-late 80's. I think I could use the 400F as an "only" bike and not feel too short changed. Bits are available (ebay and David Silver are your friends) Its a nice looking thing, too. If you are in Chch you are welcome to take it for a spin (its not insured though).
CB750's (SOHC and DOHC) are BIG: 215kg dry if I remember, and 67hp when new. CB550s are cool as well but a 400F is nearly as quick and handles as well or better.
People want crazy money for them though, a completely mint 400F sold on tardme last year for $4500 (I should have bought it...)
You might have a think about some 80's stuff: (like the VF750F I have in my garage for cheap....) something like a GPz750, Gpz900, or something like that.
Suzuki GSX750 or 1100 maybe a Katana (dreadfully uncomfortable but soooo cool). The key to something this old is condition and maintenance history.
I thought elections were decided by angry posts on social media. - F5 Dave
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