well, imps sever more of a function for melee's with Rended weapons. with max skill rended weapon will deliver almost a lvl 6 vul, so mage with lvl 7 vul isn't providing as much MORE damage over the lvl 6 as an imperil.
imperil should just about double the damage done while going from lvl 6 to lvl 7 vul may see a jump like 20 points of damage.
BUT if you don't have Rended weapons on your melee, then either the vul or the imperil will about double the damage. then landing the other spell will shoot that double to about quad the original damage melee was doing without either.
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Ag Nar
Portal Mule Master of the Loresraat
Mastering the pixels of gamedom, 1 MMORPG at a time..