I don't know if this has been posted before, but I didn't realize spikes work this way so here goes:
* Blaze Spikes, 138 INT = 15 base damage (21 damage/hit on 99 BLM)
* Same Blaze Spikes + Brew = 156 damage/hit on 99 BLM (156/10.4=15) :: This shows that base damage for Spikes is determined at the time of casting.
* New Blaze Spikes (999 INT) + Brew = 260 damage/hit on 99 BLM (260/10.4=25) :: So there is a cap at 250 INT
* Ice Spikes (999 INT) + Brew = 156 damage/hit on 99 BLM (156/10.4=15 again, 15*20-50 = 250) :: So there is a cap at 250 INT
* Shock Spikes (999 INT) + Brew = 156 damage/hit on 99 BLM (156/10.4=15 again, 15*20-50 = 250) :: So there is a cap at 250 INT

Elemental debuffs have their final tier at 120 INT, so I guess Spikes Spells are the only real justification for a hardcore INT build on BLM anymore?