/use Gnomeregan Auto-Blocker 600
/use Glyph of Deflection
Your wall of text crits for 8021.
For a while I've been giving considerable thought to BV as a mitigation stat. It isn't an avoidance stat in any way; as I said somewhere else, it doesn't affect your chance to be hit, but if it is sufficiently high (>= AC-mitigated damage) it transforms block rating into an avoidance stat. However, the kind of fights where this is the case are the kinds of fights where thinking too hard about gear to use, or really min/maxing in any way, really aren't worthwhile uses of our valuable time. They're the fights which hit for so little that you have enough BV anyway (most non-elites and normal 5-man trash) or ones for which consciously stacking BV can make it sufficiently high, which given the current BV ceiling enforced by available gear, still aren't worth worrying about too much.
For new raid content and hard-hitting fights in old content, sufficiently high BV levels to keep blocks complete aren't possible. More BV shaves damage off of, let's say, most incoming attacks. Assuming Shield Block is maintained, virtually all attacks. If you have an uncrushable set, all attacks. As Ciderhelm said, "Avoidance also helps reliably keep Effective Health high [because it protects SB charges and thus makes the BV-shaving reliable]".
This poses the problem: when choosing gear for a theoretical boss encounter where you'll take very big hits, and maximizing EH is the only conceivable option, can sufficient avoidance be included that BV can reliably be included in this EH?
Taking a very generalized look at the tanking gear currently available (consulting the EH/Avoidance list of course), it seems that there are a lot of situations (esp. head and waist) where there is one item for a certain slot which boasts the highest avoidance, and a different item which wins in both EH and blocking chance. Obviously in a lot of these cases different gemming yields the higher value in either category, but every single blocking winner is so because it has quite high block rating. In all these cases, the EH/block winner also stacks some pretty hefty BV. Generally, wherever you'll find block rating on a piece you'll find BV, and vice versa. This is what makes these items worth considering for the purposes of this particularly long post
High BV, high block rating, high EH (eg. [item]Faceplate of the Impenetrable[/item]). But hold on a minute; isn't avoidance, not block rating, required to ensure BV's usefulness as an EH stat? Well, yes, but with one exception. If that block rating makes you uncrushable, then the need for SB is negated. It should also be noted that, if crushings are off the table, hits will be less spiky and lower on average, which means the high BV that comes with this block rating gear would be even more effective at reducing all incoming damage.
The only question that remains, the one puzzle in the way of this (probably pointless) pursuit, is this: Would passive-uncrushability through BR/BV gear still allow sufficient EH to tank harder-hitting raid content?