My system crash was much worse in P5 - to give one example, I'd rendered a sequence of scenes with all the same figures etc, and had done five or six. The next one always froze the computer, normally at the end of 'adding objects', regardsless of how clean the machine was - fresh start, all other software shut and it froze at the same point every single time. Eventually, I got it rendered with a bucket size of 2.. It had even started to freeze the machine outside renders towards the end. So far, P6 is much much better - I've always been messing around when it has frozen. It's also always been Firefly that does it - the P4 render managed the same scene but it looked far worse.