How are the new stat comparisons on items calculated?

Solution 1:

The new toughness and healing listed in your character stats are equivalent to your EHP and your regen/second (when totaling all sources including regen, loh * proc * attack speed, life steal, etc).

The % changes is now purely based on how much of a boost or loss when compared to your current gear.

The example you give shows a 13.3% overall EHP gain, a 5.6% gain in life per second.

Note I've noticed the healing attribute fluctuates a lot if you have life steal on your weapon as it doesn't count until you are actually dealing damage to something so I'd take that with a grain of salt.

As for the toughness/EHP calculation, I'd also be careful as it considers dodge as part of EHP and there are many things that can't be dodged.