Whist I agree that H145 axles are like toothpicks !! - I ran a welded H145 in my coupe for a year without drama. Admittedly only behind an A14 but it was not treated kindly ...... While your car sounds a bit beyond the H145 capabilities, usually it is side stepping the clutch that causes problems. Shock loads will kill components long before the same force applied linearly.
If in doubt - go for the 29 spline H190
Cheers