In fact saying nearly on par is being generous. I'd say it's quite a bit weaker. After more bashing the proline has got all sorts of tears in it, although I repair it as I go with shoegoe. The cab seems the weakest area, overall it just flexes more than the stock.
I've actually ordered a new clear stock shell today. After looking at my original shell I can clearly see why it's stronger as there are a lot more ribs in the cab and front which gives it so much more strength. I've bashed it way more hard and it's just the rear of the stock shell that's totally wrecked on mine (rest of it is perfect still), although that won't happen any more as my roll cage totally reinforces the rear end now.