Apart from the obvious affect on performance of having 500Kg of deck cargo equivalent to about 6 Adults weighing 80Kg.
The stability issues / calculations relevant to height of crane / reach can be easily calculated by a naval architect may even be available from any manufacturer.
It is possible to do a test if you have access to the boats you are looking at by basically adding 50 Kg on the centreline of the boat then offsetting this by 1000mm and measuring the change in angle. The subsequent calculations to achieve the above are fairly simple
There is a very nice Tornado for sale at a good price in Jersey, you would get a Jetski / bike in the stern with space to spare.
The boat was tested with 12 adults plus 200kg of lead on the bow then extremity of the stern as part of the certification.