looks like the greased lightning is giving around 9% buff at 5 stacks.

i used an ability that doesnt have a range (corrosive dart) and with the elemental buff it was hitting for 1795 wihout the tactical. a rotation of just corrosive dart, corrosive grenade and rifle shot (to make sure i was getting 1 hit every second) i was getting 1955 ticks for the non crits. For grenade i was getting 1394 without the greased lightning and 1524 with.