Heeelo folks. I've finally pulled me a 6* Guardian after 1 year+ of targeting him, and I quickly took him to r4. Awhile back, I did a writeup on Guardian, and in that I made a spreadsheet of his sp2 as a 5*r5. Now it's been a bit since then, and since I finally have a r4 Guardian, I figured it'd be pretty shweet to have a more updated damage sheet.
The following sheet shows the damage of a 6*r4 Guardian's sp2 with max suicides, 3 pts in glass cannon, and 1 in recoil

Quick breakdown: Looking at the sheet you can see the number of charges when the sp2 is thrown, the damage of the sp2 with 0 crits, the damage of the sp2 if every hit crit, the *average* damage of a sp2, the damage of the shock debuff inflicted via the sp2 until recoil kicks in (only 1 tick of shock damage happens after recoil), and the *average* total damage done by the sp2 pre-recoil (shock + average sp2)
Quick analysis: Damage scales pretty linearly per forcefield charge. The average total sp2 damage goes up roughly 17800 per charge.
I've spent the past 2ish hours on obtaining the data, so I wrote this breakdown pretty quickly. If y'all have any other questions, let me know! And as always, don't forget that Diablo is the best champion in the game!