Finding neutral when engine is hot is one way for me to verify the oil to be OK for the engine.
All 10W-40 oils I have used cause very hard an mechanical gear shifting. I used those for break in only.
CB750 should use 20W-50. I think that 10W-40 was for colder temperature, max 15C.
I have tested Motul 5100 15W-50 semi. Better than Motul 20W-50 mineral and much better gearbox feeling than Motul 10W-40 mineral. Castrol 10W-40 mineral also very hard gearbox.
Motul 7100 10W-50, even better.
Red Line 20W-50, best so far.
This in my K6.
Spectro Heavy Duty 20W-50 mineral caused sticky clutch. Out with 1L and in with Q8 SBK racing 10W-50 (cheap synth) made it really good. Gears shift very smooth!
In my K2.
Both Red Line and Spectro have high amounts of zinc and phosporous.
I have ordered Eurol Harley Davidson 20W-50 oil that is very cheap. It cannot be high quality synth as Motul 7100/300 or Red Line (esthers) but well worth to be tested. The gearbox when hit will tell!
I have done my own semi by mixing 2 Spectro 20W-50 mineral, 2 SBK racing and 1 Red Line 20W-60 to be used in My K2 stock spec.
The latter for my K6 summer 2018 where we had over 30C during a long period of time. I ordered a box of 20W-60 to my hotter running K6 with 1000cc Billet block.
I'm convinced that CB750 run well on V-Twin 20W-50 JASO MA oils.