Axles Breaking 99 Boxster

[3RotorRx7]

I have had 3 axles shear right at the splines on the right axle in the last 2 events run. Basically 3 broken in 30 or so launches. Twice at the outer CV and once at the inner CV. This happens during a hard launch in Pro Solo autocross. Car is 2100 lbs plus driver. 315/30/18 on 18x11" rear tires. 2.7 liter motor, but also broke one with 2.5 liter motor. Running 2.5 liter 5 speed and axles.

Trying to figure out a bigger axle swap. Noticed the Tiptronic axles are larger at the spline by 80/1000" of inch, but would have to cut them to make them correct length. Does anyone have a measurement of the axle diameter of the Boxster S axle at the splines of the CV.

2.5 manual axle: 1.142"
2.7 tiptronic axle: 1.222"
996 Boxster S' axle: ?

Thanks,
Erik