The order doesn't particularly matter because, as you said, it's multiplicative.
That said, you might like to peruse this:
As for your interests in Frost vs Blood, I'm going to side step the numbers (hopefully this will offer the tools to do that math yourself), and get to what I think is more important.
Frost will take less damage than Blood, period. What is lost and is hard to quantify, is the self-healing from Blood.
The difference may actually be more severe than you might think. I did some tests in Ulduar, blind studies on healer perceptions, and compared parses. The results were something to the tune that, the healers felt like I took less damage as Blood, where parses recognized that I actually took upwards of 20% more overall (that is *NOT* the actual difference with just the passive buffs though mind you). The self-healing from Blood, especially in the hands of a user who's experienced, will be a significant value on the apparent damage taken.
*Also, here is a handy web app, to quick-calculate reduction from armor: World Of Warcraft Armor Damage Reduction Calculator