The boat I'm looking at is the one in this thread:
Considering an SR5.4
It's got removable bungs so the hull can be flooded or not (will probably use it mostly flooded for the stability with dropping divers \ taking photos etc.).
As for 'rough' I guess it's all relative to the skipper and will depend on the bit of sea, but say 1m waves, either short chop or rollers as an example - how easy is the SR5.4 to drive compared to others of a similar length? Bearing in mind as well that I'm on a budget of £5-6k, so £100000 boats are out the question