Bob, we fully appreciate error budgets and propagation of errors
analysis. Never the less if most VFR traffic is 'trying' to fly at
the correct hemispheric altitude (especially those who tend to fly as
high as reasonable) , and we bias our choice of altitude to be under
the mean altitude of the others, we will probably have reduced an
already small risk to one even smaIller.

I don't don't know the statistics for altitude holding accuracy in the
less than 12000 feet VFR XC world, but would not be surprised if the
S. D. is the order of 50 or 80 feet.

I also don't know the stats on near misses (or worse) during the
cruise phase of VFR XC but am trying to find out. Near misses are
going to be very much under reported, aren't they?

I've offered an argument for not staying at the exact altitude during
VFR XC , and am interested in learning some reasonable rebuttals. I
did offer one for not maintaining the exact expected altitude and hope
someone can offer compelling reasonings as to why those reasons are
not valid.