No one has tested out this, so the answer is just theory.
Based on memory (not 100%)... +600 max life is equivalent to 200 Vita stat points @ level 1 (3 life points per stat point)... the only difference, you don't gain hitpoints per level you go up when you have actual points in vitality.
I use 0 ee armor when I solo. During my runs, I notice that monsters deal around 0-150 dmg around level 45 upwards... my base Vita is 100, my base Int is 60 and I wear Plate with 38 Int / 16 vita @ level 45 to 71. When facing EPs, the dmg changes of course, there are other factors not considered, like them crit hitting for 150-500, also multi attack mobs, and the worse one is Pulfulgore... he has an extremely high QD and attacks rapidly which feels like a 5+ hit combo.
Note: the damage I posted is based on Solo and memory of damage noticed, so it may NOT be 100%... and my stats enhance my defense and I also use Salvation... I don't use regen gear on my Guardians because I heal, I use heavy weapons and in the last 4 test runs from 55 - 70, it takes approx 1 hour per 5 levels, posted below for your own conclusions:
Not conclusive enough material, still could not take full count of Quick Draw activating, but, will just post results anyway.
Results will show after comparison vs other items.
Please Note that I am using identical gear;
Mythical adamantium longsword, Damage: 64 to 646, +124% Enhanced Effect, +246 Max Mana, +1% Life Steal, +5% Mind Numb, +3% Critical Flux
Angelic tempered diamond plate mail, Physical Defense: 51 to 154, Magical Defense: 0 to 23, +16 Vitality, +38 Intelligence, +8 Life Regen, +2% Mind Numb
Arcane focused heal XIV, Heals: 138 to 166, +3 Vitality, +1% Experience Gained, +1% Damage Return, +1% Critical Flux, +11% Quick Draw, +1 Jubilance
Magical wild heal XII, Heals: 48 to 481, +107% Enhanced Effect
Code
SS Huntress = Lvl 55 = Str 44 / Dex 13 / Int 61 / Vit 100... Gear Adds: Int 38 / Vit 19: = Total: Str 44 / Dex 14 / Int 99 / Vit 119
Level 55 - 60: Time: 57m 09s - Actions: 1712 (Att+Heal) - Total Dmg = 528078 - Total Heal = 115796 - Evil Presence = 1
Level 60 - 65: Time: 1h 11m 55s - Actions: 2156 (Att+Heal) - Total Dmg = 630323 - Total Heal = 170979 - Evil Presence = 2 + Treasure Pest
Level 65 - 70: Time: 1h 20m 43s - Actions: 2471 (Att+Heal) - Total Dmg = 734120 - Total Heal = 228124 - Evil Presence = 2
SSPro = Lvl 55 = Str 44 / Dex 13 / Int 61 / Vit 100... Gear Adds: Int 38 / Vit 19: = Total: Str 44 / Dex 13 / Int 99 / Vit 119
Level 55-60: Time: 0h 59m 11s - Actions: 1747 (1546 [att] / 201 [heal]) - Total Dmg = 534213 (0 / 346 / 1360) - Total Heal = 119898 (42 / 597 / 1360) - Evil Presence = 2
Level 60-65: Time: 2h 45m 55s - Actions: 1768 (1434 [att] / 334 [heal]) - Total Dmg = 534802 (0 / 373 / 1336) - Total Heal = 144936 (20 / 434 / 3222) - Evil Presence = 2
DavidWilson: Lvl 55 = Str 44 / Dex 12 / Int 61 / Vit 100... Gear Adds: Int 38 / Vit 19: = Total Str 44 / Dex 12 / Int 99 / Vit 119
Level 55-60: Time: 1h 04m 45s - Actions: 1871 (1627 [att] / 244 [heal]) - Total Dmg = 560520 (0 / xxx / 1350) - Total Heal = 118473 (31 / xxx / 1940) - Evil Presence = 3
Level 60-65: Time: 1h 06m 53s - Actions: 2048 (1754 [att] / 294 [heal]) - Total Dmg = 603634 (0 / 349 / 1350) - Total Heal = 174053 (35 / 403 / 2703) - Evil Presence = 3
Level 65-68: Time: 0h 51m 40s - Actions: 1536 (1248 [att] / 288 [heal]) - Total Dmg = 449384 (0 / 399 / 1464) - Total Heal = 145848 (36 / 477 / 2548) - Evil Presence = 2
Level 68.25-68.84: Time: 0h 11 00s - Actions: 341 (276 [att] / 65 [heal]) - Total Dmg = 96901 (0 / 351 / 1093) - Total Heal = 36329 (41 / 559 / 2595) - Evil Presence = 1
Level 68.84-70: Time: 0h 21 56s - Actions: 675 (521 [att] / 154 [heal]) - Total Dmg = 184909 (0 / 355 / 1232) - Total Heal = 69999 (37 / 455 / 2313) - Evil Presence = 4
SSPro: Lvl 60-65 Time is debunked as I was totally drunk during that run and doing other things. Completed 65-71 without taking notes.
DavidWilson: Lvl 60-65, did some welling, in between, did not take the information, also stopped at intervals between 55-60, thus averages were incorrect.
DavidWilson: Lvl 68.25. Server Shut down notification. No time to complete.
DavidWilson: Lvl 68.84. Overrun by Slugslider, did not want to regen and ruin time, so I remade: Note: I haven't regen'd in every test, don't want to start.