Here's what I learned in going from Hobie-14 to Hobie-18 to Hobie-20 to NACRA 6.0:

Similar things happen with variations that are due to the differences in designs. For example - on the Hobie-14 if you headed up in a puff to depower going upwind you could flip the boat over backward because the sterns had little bouyancy - you had to play the sheet. On the 18 and above heading up in a puff becomes an option (not to start arguments over which is the best way). You learn the diferences through looking at the design and time on the boat.

The main thing was this - things happen faster. You have an expectation of events happening at a certain speed in your current boat, and when you get on a faster boat it can get ahead of you because you are not expecting things to happen as quickly. The first time out on the 20 moving up from the 18 my crew and I had the boat get ahead of us a few times until we got used to things happening faster. It didn't take long to aclimate, but it could freak out the timid. I actually ended up in irons a few times tacking because the boat responded so much faster to helm inputs - I used the usually truck-driving approach that worked on the 18 and found the boat tacking too quickly, then backed off the helm because I thought I was tacking too fast which then left me in irons. I had to laugh at that one...

Spin sailing adds a whole other level to cat sailing that is just plain addictive IMO. Take your time, figure things out, enjoy the ride!

Start out in moderate conditions and get used to the new sensory inputs - you'll love it.