Worthwhile thread on another forum:
http://alltrikes.com/elgg/pages/view/17715/powerline-avoidance-strategy
http://alltrikes.com/elgg/pages/view/17715/powerline-avoidance-strategy
I flew an 18A from Tulsa to Houston some years back, and noticed transmitter towers disappearing above me into the overcast (obviously taller than the local ceiling on that day). When you worry about guy wires, you have to plan for them reaching out from the full height of the tower, from a top that sometimes isn't even visible. I give those things a VERY wide berth. They scare me more than "horizontal" power lines, whose locations I'm more accustomed to anticipating.