Thanks. I think 8 hr rides turn into more of an "adventure" than a hard training ride. Not sure how many folks can push a decent tempo/wattage/HR for 8 hrs (maybe some though).
I'm still not completely convinced that riding 6 hrs 3xmonth benefits you more than HIT if most of your events are no longer than 3-4 hrs. I know w/ marathon runners though, they do high mileage b/c there are indirect benefits physiologically (mitochondria, oxygen uptake, etc), but they rarely do long runs more than about 2-3 hrs (maybe more b/c of the recovery aspects are harder).
Appreciate everybody's input on this - I'll try Hunter's points for his "Next Level" article.