For a PPL(H), I don't think for one minute that a 600' cloudbase is suitable for departure. You say that with the 500' rule, 100' is adequate for keeping out of cloud? There are many PPL holders who can't even fly within a 100' error. Not saying all but there are a few. What if their altimeter is incorrectly set? Wouldn't be first time ether. They look at 500' on Alt an OOPS, in cloud. Also flown with a couple of PPL's who quite happily kept climbing out of the circuit into cloud. It took a while for them to even realise the error of their mistake (too long to survive solo anyway) but anyone who takes off with only 100' to play with might not be the best person to be flying. It doesn't take a brave man to make a safe decision. !!