Elder Conc/Burning Helmet or Memory Vault for LL RF Templar?

I can't quite decide BIS helmet for my low life righteous fire templar.

Which is better?
An elder helmet with gems supported by level # concentrated effect/burning damage or memory vault?

The former probably gives more dps and allows 6L for a secondary DPS skill (scorching ray).

I'm actually uncertain why some guides recommend MV as BIS. I know it gives a huge amount of armour but in my case I calculated I can potentially fit in determination aura at the expense of losing aspect of spider.

I couldn't figure out how to calculate the additional dps from aspect of spider DPS but it doesn't seem to be much.