For those comparing the 2xGR opener and the single GR opener, you can't just say "You get two GR's vs. One". More like you get roughly a half of a GR, meaning that this is only 50% effective. You'd have to end a fight on that 10 second timeline in order to gain any benefit from using GR first.
You also need to consider the rough .5 second delay that you are delaying your first GCD.
So basically we are comparing 50% of a GR vs. 25% of your average GCD potency. It is roughly 90 Potency vs. ~46 Potency (average GCD potency).
We should also compare the potencies of the fully buffed GR vs. The GR with only half buffs.
Pre-Pop GR would have: (180 * 1.2(IADII) * 1.3(GB) * 1.1(B4B) * 1.15(HE) * 1.2(RS)) = 426 Potency
Not Full buffed GR w/ WF : (180 * 1.2(IADII) * 1.3(GB) *1.05 (HS) * 1.05(HC))/.9 (Piercing) = 343 *1.25 = 429.975
vs.
Fully buffed GR : (180 * 1.2(~Dex pot) * 1.2(IADII) * 1.3(GB) * 1.1(B4B) * 1.15(HE) * 1.2(RS) * 1.05(HS) * 1.05(HC))/.9 (Piercing) = 626.59 * 1.25 (WF) = 783 Potency
From here, we just need to add the two GR's to get their overall value. Then take the fully buffed GR, add half of a GR and add 1/4th of your average GCD. We can then compare the values to see what is better.
429 + 426 = 855(2x GR) vs. 783 + 90 + 44 = 917(1xGR)
So 1x GR may still be better. I would need to put it into a spreadsheet to see exactly which one is better.