Just going to pick on the oxygen thing.
Human performance decreases with decreased oxygen in the the blood - a pO2 of <90% produces measurable decreases in performance similar to intoxication or fatigue. Most non-smokers without lung disease are at this level at 10,000'. Smokers and those with lung disease are at worse levels and the effects are cumulative with fatigue etc.
The effects of hypoxia are felt on night vision at even lower altitudes.
The reason the USA have the 12,000 limit to allow non-pressurised aircraft get over the highest parts ofthe Rockies, ans was intended only to be used for the period of time required for terrain clearance. I believe there was considerable pressure from AOPA USA (correct me if I'm wrong) on this "relaxed" level, but there is not good medical reasoning behind it.
STC'ed portable oxygen sets are not expensive and will save themselves in fuel costs fairly quickly and small pulse oximeters are available for ~ $400. I regularly fly in the flight levels SE IFR on portable O2 and find it comfortable and covenient. BTW pax don't need to share in it <FL140!
I agree with much of the rest of Dick's posting and addiotionally mourn the decrease in access to airports for GA as a result of privatisation of what is essential transport infrastructure.