I've never really bought the 'spike damage' argument when it comes to avoidance. If you just stack health you take the same spikes constantly.
I was a healer for all of TBC (MT in Classic and WotLK) and I never had a problem with avoidance. Ever. I would much, much rather have a tank take 40k damage every 6-7 seconds and occassionally 2-3 hits in a row rather than always taking 40k damage every hit, every time, for the entire fight. The 'spike' argument really only applies to healers with short attention spans that have no clue how tanking works, who wander off to the other side of the room because they think the 'tank is fine' because he's not taking any damage.
Unless avoidance somehow increased the size of the spikes, there is no issue. Stacking health instead of avoidance just means you're taking massive damage all the time instead of some of the time.
You seem to be completely missing the point of what I've been saying. The situations currently most likely to kill a tank are unavoidable, tanks are supposed to survive, therefore I pick the stat that helps me survive, which is EHP right now. Dodge does nothing to help me survive an impale, or freezing slash, or ferocious butt, or enraged bile spray, etc. etc. etc. etc. etc. /broken record.
Your aforementioned tradeoff of 8 stam for 20 dodge rating just doesn't seems pretty non-optimal. You're free to gear however you like, and if it seems to work then more power to you--but from a gearing perspective, I can't see much logic in doing so unless you were really struggling to meet some specific HP threshold that you weren't at yet.