For Protection, I think 80%-100% armor at level 6 is plausible.

As for Force Shield, I honestly could see a lot of variety for this skill.

1. Turn it into a Mana Shield like PL's. Pretty self explanatory.

2. Increase the damage that it could absorb. After the shield breaks, your armor is increased by 50 per level for 3 seconds.

3. When shield is activated, instead of getting damage, you get healed by (n)% of the damage you are taking. Lasts for (n) seconds. % healed increases per level and duration increases every 2 levels.

4. Increase armor by (n) for (n) seconds and reflect (n)% of damage received.

I could probably put some more but those are the ones that I think would work the best with their current skills.