Qwayfe

Two questions here:

Firstly, there was mention in the arcane thread that the 20% Arcane Blast damage buff only applies to base damage and does not scale with bonus damage. Anyone confirm/deny this?

More importantly, I'm wondering about the mechanics of the 4 slot bonus.
Is there a latent cooldown on the bonus?
Does the bonus stack?

In working out the gear I want from the tier 5 instances, I'm looking at an option between taking the set for its bonuses or gaining 8 spell damage and 44 hit elsewhere. So, yeah, any help would be appreciated.