Those little 400/4's were very sweet bikes and are quite valuable now.
I had the little cousin to that bike, the 350/4. Further proof of PW's point is the following story about that bike.
At the time I had a friend who would frequently borrow a mutual friend's CB900. It was the only bike he ever rode. Pretty nice bike. Quite powerful. Dual-range tranny, so it was effectively a 10-speed. Never could quite figure out why they did that, but they did.
We used to race on a twisty road from Olathe to DeSoto to meet at the Dewdrop Inn for lunch. About 15 miles. Loser buys.
The only time he ever beat me was when I overheated the bike on an extremely hot day. I could feel the symptoms of overheating (also easier on a smaller bike) so I pulled over.
I usually beat him not by seconds but by minutes. That bike probably topped out at about 80 mph while the 900 was good for well over 100, but since my capabilities were greater than the bike's, I could do most of that 80 mph all the way to the Dewdrop, turns and all. My friend on the 900 wasn't 10% as capable as that bike was, so it wasn't a fair contest.
He sure did love to goose it on straights when we rode together, though, and leave me in the dust. Any a-hole can open the throttle.
Well, maybe not, actually. I used to be quite a terror on my Suzuki X6 Hustler (250cc). It was not uncommon to smoke (literally) the Honda 750's in stoplight to stoplight races.
Disagree with you (or whoever it was) about the dirt being the best place to learn. It's really a whole different ball game. Dirt riding puts a lot more emphasis on controlled drifting and handling an airborne bike.
Controlled drifting on the street just overheats tires which end up going away, if the bike can even do it. Most will drag the pegs (even dangerously, as in levering the tires right off the road). And of course, I don't need to say anything about airborne street bikes. <g>
I might be biased. All I really ever learned from dirt riding is that falling down really hurts when it happens and starts hurting again 30 years later.