Hi Dwight,
I've been putting in a lot of deer fence up here in the Comox Valley over the winter.
We have the same kind of deer problems as you folk and the 7 foot 6 inch farm wire is the standard here. It seems to be more than enough to keep the little rascals at bay. (For the benefit of readers not familiar with this area, we're plagued with a remarkably small species of deer here. What they lack in size, however, they more than make up for with numbers.)
Most of the work I do is with treated wood post. I like to go 4 to 5 inch 10 footers on my corners and braces and then 9 foot 3 to 4 inch on my line posts at 10 foot spacing.
Our soil conditions are pretty variable. It can go from clay to sand to gravel to rocks bigger than your head in only a matter of feet. Like your ground, we go from really soft in winter to rock hard in summer. I won't build a fence here unless the client agrees to double bracing.
If you're going to hang foliage off this fence I'd recommend going with deep, deep corners and braces and using the high tensile wire.
The BC Government Ag site has a pretty good pdf brochure on deer fencing. We don't need the height they recommend and the prices are a little outdated but it gives a pretty good overview of what needs to be done.
Slim