'twas an SR4.
so on a normal 550 the difference would be 1.3 metres of length,
but my Gemini was factory built short for a specific purpose and is 51cm shorter than a standard 550. So the difference in length was 80 cm, and I think any difference in length will help the sea keeping - certainly the ride across short chop is better. The tubes are bigger on the Gemini, you feel more like your sitting in the boat rather than on the boat with the Avon.
I think the Avon was a softer ride at slower speeds.