I'm not familiar with any point and shoot system but my advise is to go with the one that allows you to have a wider angle of coverage as possible ,because for good results you need to get close ( which you will probably get at Silver Banks ) .
Don't worry about the size/weight of your system , the whales will swim or get close to you . You will not be allowed to swim to them and if you do it most probably they will go away .
Being in the water close to the humpback whales is an experience that for sure you will enjoy . Good luck