I've made a damage calc for this.
As Kitty said, it's pretty much guaranteed that on-element is better.You NEED to get Garuda Hammer MLB, and leave yourself with enough mats to FLB it later (some Silver and Gold mats). That is BY FAR the most important thing in this event (and getting MLB Garuda if you don't have full SSR MLB Eidolon Grid yet).
But in general, the more you farm, the better for you.Why do you need Grails...?
Are you aware that SR weapons are 35 points each, per skill level? In other words, you feed a R to SR weapon, and it's worth 70 points. Then you feed it two Rs, and it is worth 105 points. Then you feed it three weapons, and it is worth 140 points.
SSRs require 20 points per slvl, so slvl 11*20 = 220 points. That's one SR4 and 8 Rs (for a total of 14 Rs and 1 SR).
You can get plenty of fodder for SR weapons by farming Standard and Expert Disaster Raids.