So I'll just keep using the tanking spreadsheet from mmo-mechanics? I'm hoping it's still up to date, since I don't think it's been changed since 1.2.
As long as you've updated the armor value to reflect 1.3 nerfs, it's still an accurate way to gauge pure minimized damage taken.
What it does not reflect is the "break even" point where END can be sufficiently valuable to consider (which is why the 27B mods are so good... you have a large enough pool that the END, though less useful point-for-point, becomes relatively valuable enough to use the higher-total-budget-but-lower-mitigation mods at the DG tier).
KeyboardNinja has posted some really good stuff based on boss damage data. I started an initiative to try to build a more accurate stat optimizer out of his work + the original spreadsheet, but it's a huge pile of work and RL has gotten in the way. If I ever get it finished I'll publish it, but it will likewise be constrained by its data (just as the old spreadsheet doesn't account for actual boss data, this new one would be limited by its boss data).