I noticed the same with Hi-Fi VHS, I believe that beta is more superior in terms of quality and reliability, VHS Hi-Fi tends to be more sensitive to slight impurities/wear in the tapes and can "flicker" or drop back to the mono track more so than a beta does. I have only just Migrated to Beta Hi-Fi, the results are impressive, I chose the Sanyo because it is easy to work on and I had another machine here for spare parts. Cost me $150 for the Broken Sanyo VTC-M40 Beta-HiFi (belts/idlers, lube, clean etc), hard to get at that price (especially with good hi-fi heads), they go for much more in working order. If you can turn the tracking dial all the way from the far left to far right and not lose the hi-fi track, this is a sign of good hi-fi heads with low hours.
When I was a teenager I used to push 8db on an old national NV-850 Hi-Fi VHS machine whilst recording film clips off analog tv, I didn't really know about recording levels, it just sounded louder, but somehow still clear and distortion free. I saw some pre-recorded Hi-fi VHS tapes hit 10db (one I can remember is Prince's Purple Rain) and remember being blown away by the sound from that movie, was also cool to see those last two increments on the meter light up for the first time.
That note you made re slightly lower peak signals, do you mean it sounds better at a lower level? I thought the louder you recorded it provided it was distortion free the lower the hiss levels as the recording loudness would drown the hiss out? I'm still learning here. With cassettes I stick to +2-3db for ferrics, +4-5db for chromes and +6-7db for metal, this is with a HX PRO capable machine. I don't know what Nakamichis are like but I plan on obtaining a BX-300 in the future, I hear these don't have HX PRO, does that mean you have to record lower db with them? Either way it doesn't bother me really.
I look forward to seeing some of your 70's car gear, let me know and possibly send a link if you get a chance.
Great talking audio with you =).