Chroma is complex to calculate given Vex Armor's mechanics, first we need to calculate a few things for that:
Shields lost to max: 400
Base shields: 300
Shield Regen Rate: 15.0+(0.05*300)=30/s
Shield Regen Delay: 3.0
Time to 100 Shields from Depletion: (100/30)+3.0=6.333 seconds
Duration: 18.1 seconds
Average Mult: ((6.333*1.0)+((18.1-6.333)*3.5))/18.1=2.625
So in a perfect world where all of chroma's shields are dropped immediately and then he's given time to regen back to 100 before those are then dropped each time he refreshes Vex Armor: he'll have a minute-wide average of 2.625 total armor multiplier before power strength.

We also have to account for the massive energy cost of Vex Armor and Elemental Ward:
Recast Time: 18.1
Casts/Minute: (60/18.1)=3.314
Energy Cost/Minute: (77.5+116.25)*3.314=642.087
LTER Energy = 400
Average Energy Pool = 600-(642.087-400)=357.913
So assuming Chroma drops one Large Team Energy Restore per minute for every minute of the match and stays within range he'll have an average of 357.913 available for Quick Thinking to use at the start of each damage taking event.

Ice Chroma EPH (Explanations for odd values to follow):
HP: 300
Armor: 350
Energy: 600
Average Energy: 357.913
QTHP: 300+(357.913*2.4)=1158.991
Power Strength: 1.99

Additive:
Steel Fiber: 1.10
Armored Agility: 0.45
Arcane Guardian: 0.60
Elemental Ward: 1.5(1+1.99)=4.485

Multiplicative:
Vex Armor: 2.625(1+1.99)=7.849
Stone Shape: 0.12

Total Armor: (350*(1.0+1.10+0.45+0.60+4.485))*(1+7.849+0.12)=23967.410
Total Damage Reduction: 23967.410/(300+23967.410)=98.763
EPH/Minute: 1158.991/(1.0-0.98763)=93693.69


Valkyr also has her complexities given Hysteria and how it operates.  Since the focus here is optimal EHP/Minute we're going to assume that Valkyr is also pooping out one Large Team Energy Restore per minute and staying near it.  Seeing as the cost of warcry is basically non-existent with Eternal War we'll ignore that and instead look at the optimal Hysteria time possible while still maintaining her max energy for the start of a given damage taking event:
Excess Energy/Minute: 400 (from LTER)
Min-Drain: 4.375
Max-Drain: 26.25
Time to Max: 10s
Drain increase rate: (26.25-4.375)/10=2.187/s
Drain to Max: 142.165
Time to consume excess: 10+((400-142.165)/26.25)=19.822
EHP multiplier: 1.0+(19.822/60)=1.330
This means that since Valkyr is completely invulnerable for 19.822 seconds out of every minute given the max power-strength build's efficiency while still maintaining 600 power at any given time for the start of a damage taking event she has a 1.330 multiplier on EHP/Minute

Warcry Valkyr Prime EHP:
HP: 300
Armor: 700
Energy: 600
QTHP: 300+(600*2.4)=1740
Power Strength: 1.99

Additive:
Steel Fiber: 1.10
Armored Agility: 0.45
Arcane Guardian: 0.60

Multiplicative:
Warcry: 0.5*(1+1.99)=1.495
Stone Shape: 0.12

Total Armor: (700*(1.0+1.10+0.45+0.60))*(1+1.495+0.12)=5766.075
Total Damage Reduction: 5766.075/(300+5766.075)=95.054
EHP/Minute: (1740/(1.0-0.95054))*1.330=46789.324

Note that both frames have a FAR higher result (quickly approaching infinity) when you factor other forms of energy regeneration and how ridiculous they can get.  Also note that both frames are running maximum power strength, steel fiber, quick thinking, and armored agility, so there's not much room for anything else in there, so these are highly specialized builds.  From testing: the Valkyr numbers are far more stable while the Chroma values listed are more of an "ideal state" shields regen and duration.  Realistically you're better off making a balanced build for him rather than dumping 100% into power strength and going so far negative in duration/efficiency.