I hear ya; but I made an entry in the 'other one' too and the only time I've been in the Roadie forum in the last 2 months was when I was looking for the other thread. I think there was just one thread and it got bounce around and ultimately robbed, or maybe deleted by mistake and re-started?

Anyway, the gist of my answer was that 170s isn't all that extreme for a young-un. The club cyclists I know that push their HR up that high are typically going much faster, though -- on the order of 22-25 mph. More zone 4 and 5 work is indicated.