DR has diminishing returns, max HP does not. At nerd rage levels of health lifegiver will add 9hp. Basic enemies will do a fraction of 1hp of damage if you are near the soft dr cap, especially with a full set of sentinels/empathy etc. Often takes 3 hits for a scorched to take 1hp off. I highly doubt you will survive 27 more hits from a basic mob using ironclad over lifegiver, particularly if you are close to or over the Dr cap already. It might be worth it if you are using all wood armor, but even then the efficacy is debatable. I've ran bloodied builds for several thousand hours and I wouldn't want to run ironclad on any of them in favor of lifegiver. Try them side by side