30% block is not an effective option. Dexterity adds linearly to block percentage. Just for example, say that one point in dex gives you 1% block. Going from 10-20% block takes 10 stat points (effectively 20 hps). It blocks 11% of the unblocked physical damage. Going from 50-60 takes 20 hps and blocks 20% of the incoming physical damage. That's why people always push to max it or put nothing in. The more dex you've invested, the more effective each additional point becomes.
Most deaths in hardcore come from Physical enemies, who have a number of ridiculously nasty, pretty much unmitigatable mod combinations. They can spawn with enchanted: Might, Conc, or Fanata; Cursed, Extra Strong, or Extra Fast, and each of those multiply off of each other. Three mod Cursed, Extra Strong, Fanata enemies will be doing easily 10x the expected damage after you're cursed.
The general consensus in the HC community is that giving up 20 to 25% of your hitpoints to attain 75% effective damage reduction against the most deadly enemies is the correct decision.
The deadly elemental stuff is pretty much FELE (did they fix this? I really haven't had the guts to test it, I let my merc deal with FELEs) or Conviction+Two or three other damage mods. Three times as many of the aura enchanted bosses will kill you with physical. So you're giving up at most 25% elemental survivability to triple your physical survivability (-25% hps, then 4x as much effective hp).