For reference, I was able to do HM garuda in a DF group with 6600hp in Defiance on my alt WAR. I died a couple times (we 2 shotted her), and the sentiment that the most worrisome time is the add phase is correct. If you are skilled, you can probably get away with 6000-6200 (?) as long as you have good healers for the add phase. The rest of the damage is negligible, especially if you avoid slipstreams, which a knowledgeable healer will thank you profusely for.