From memory the wording in the regs says something to the effect of 'should make appropriate calls if you're likely to bother the traffic in the CTAF'. Helpfully though there's no height limit to the CTAF. I'm fairly sure that the folks overflying in the flight levels don't bother talking to every CTAF.. so practically my approach is if more than 2000-3000 above, don't bother.
However, if the CTAF takes RPT/faster traffic, (Mt Gambier for example), I tend to make sure I have the CTAF on Box 2 at least, and think about where their approach path might be - i.e. am I likely to come into conflict with them (possibly well outside normal CTAF limits), and if so, talk to them.
To answer your other question, I tend to prefer altitude changes to maintain VMC for the simple reason it makes the nav easier than putting in doglegs. That is, unless there's some reason why not, like a few thousand tons of rock in the way, or lacking outlanding options.
Last edited by Mark1234; 21st Oct 2010 at 08:55.