Ran out of stanage bay about 6m months ago alongside a 6.8 walkaround patriot in my 5.6m sharkcat. Also in our crew was a 2400KC and a 6.2m centre conole KC all left ramp at stanage about the same time.
the haines went well but my Sharkcat and the 2400 were a fair bit quicker in the rough heading out to Hexam group in fairly ordinary conditions. I'd say 10-15km/h faster roughly.
My mates 6.2 CC kevlacat flew past me and the 2400 like they were standing still though. Unreal how good it is in the rough without a cab on it.
It was a good indication of sea keeping abilities for the 4 boats. As we all were running in the same direction for a fair while.
Now as I mentioned earlier, ride isn't everything in a boat.
If you only travel 20-30km out then other factors should weigh higher in your boat purchase