Hexblade

[ForceUser]

This was specifically answered in the newest FAQ, available at WotC. Mithril (and ileafweave, etc) armor counts as one type lighter for proficiency purposes.

Yeah. I think that's lame. WotC doesn't always get it right.

 

[Particle_Man]

Surely the most relevant factor for the OP is how his own DM rules armor. Does his DM follow the FAQ/Sage Advice? If so, it doesn't matter how many other DMs houserule armor. Does his DM use his own house rule? If so, it doesn't matter how many other DMs follow the FAQ/Sage Advice.

Back to the Hexblade: I would avoid spells that require saving throws, as you will be "behind the curve" except for those instances where your spell-victims are the same as your curse victims.

Another popular route is to go into Dragon Disciple.