Anyway now people will sign up for the loosing side so they can get into 75% more easily.
At time of writing the average tonnage delivered in the Mahon CG is 8128t/player, whereas the average delivered in the Kaine CG is 8230t/player.
If you want an easier job getting to 75% then the Mahon CG might still be the one. (Though the difference will almost certainly be <1 extra trip in a T-8, and anyone with a fleet large enough to benefit from having ten niche-build power distributors rather than five is going to have no trouble getting into the top 75% either way)
Weird, because my impression is that majority of people signed up after the weekend
At the end of the first day it was 1356:433 (~3:1)
At the end of the second day (start of the weekend) it was 3515:1007 (~3.5:1)
By the end of the weekend (4th day) it was 7369:1841 (~4:1)
By the time of the announcement it was 9120:2253 (~4:1)
New signups since the announcement in this thread are 762 for Mahon, 255 for Kaine, which is back to the 3:1 ratio seen on the first day.
So we can hypothesise from this that the "correct" ratio for the CG in a fair fight would be a roughly 3:1 win for Mahon, but people joining the side which was already winning made it a 4:1 win.
Or in percentage terms: 75% back Mahon normally, but 80% back Mahon with an extra reward.
Which means that the number of Kaine -> Mahon defectors as a result of the reward is just 5% of participating CMDRs. (As noted above, the average hauling rates are near-identical for both CGs, so those 5% are likely distributed pretty evenly across the reward tiers)