If you are over 25 and have a Motorcycle endorsed license, AND you have access to Ducati Demo rides, or BMW, take a Ducati Monster 600cc range bike out for a spin. After that, you will have a frame of reference on good handling. I've ridden the GT1000, Monster 800, Multistrada 1200s...BMW F800GT, and RS1200 Bagger.
Except for the RS1200, the other three bikes handle impeccably. They are cool, calm, collected. Will take turns faster than most people can stand, and feel solid and stable bot slow and at speed.
My NH750 handles well for it's era, but after riding those other bikes, well, it's like the difference between a Lincoln Town Car and a Miata.
The problem, as someone mentioned before, is if you have never ridden a good handling bike, or even your own in stock, well maintained condition, you don;t realize how detrimental most suspension mods are to handling.
If you read about bikes, the manufactures work pretty hard to tailor the suspension and chassis. The frame is a part of the suspension. Putting very strong fron forks, like a GSXR fork, on a CB350 or 360, puts extra stress on the front steering neck and chassis rails. Add to it that many "builders" cut off frame parts (rear hoops, and such, flanges on pressed steel backbone), the frame take more stress than it was originally designed for. If you could watch the steering neck while you ride, you can see it moves and bends when hitting bums, and curves, etc. The reason there aren't more issues with these mods (IMHO) is that most of the cafe racers built are so uncomfortable to ride, that they never really are ridden much.
Look at Bradj's bikes. He isn't just cutting off things and bolting on reaersets. He is adding bracing and tubing to handle stresses. So Bradj, if he ever finishes any of his projects, is doing something much different and better than the majority of "builders".
A CB750 is designed to handle the forces and inputs on the chassis as designed. i won;t say that lowering it is going to make it break, but it adds stresses in a new way, one that the chassis isn't made to take. Generally what happens, is not catastrophic failure, but a chassis that flexes more, and causes wobbly handling, tank slapping oscillations and certain speeds, and such.
Most people are not designing cafe racers, but assembling them....The bikes end up poor handling, uncomfortable, and most times, for sale....
Not many people (but there are a few here) know how to actually improve the handling and reliability of the motorcycle. Take it slowly. You can enjoy riding on a comfortable, reasonably handling bike. Good shocks, progressive springs, fresh, properly weighted fork oil, good swing arm bushings, wheel alignment, and proper spoke tightening and wheel runout, and your bike may not look as delicious as some of the racers here, but it will be faster in the turns, run reliably, and you won't have a crick in your neck for leaning over the tank all day.
You can paint and personalilze the bike, make it your own, without destroying the functionality that makes riding fun.
All this is my opinion, I have no statistics or proof of the above....However, I have been riding since 1972, and I have a slight experience as a diesel mechanic and as a mechanical engineer. XB33a, Teazer, o1marc, Alphadogchopper, bradj, CrazyPJ, and quite a few more, are well experienced, and if you notice, share pretty much the same view.
there's a good saying: You can learn from others mistakes, or learn from your own.......
The bunch of us, as a whole, have made quite a few, and like to help you guys not make your own. We may not always agree, but we wouldn't be speaking out if we didn't know and experience many of the errors we try to help others avoid.
