we've done quite a lot of "cruising" in cat's over the last few years (Hurricanes, F18's, Tornado's) including a few big channel crossings. Last year we made it to Alderney from Essex, shame we didnt quite make Jersey.
We're a bit quicker than you. plus we can sleep on the tramps... but essential the same thing!!
My advise would be for long distance crusing, one RIB to two dinghies and lots of spares and tools. We've had shrouds, sails, rudders and crew break, and it's best to be as self sufficient as you can. When towing in and out of marina, or when the wind dies, two cats with the one RIB works well.
We use a 6.5m rib as a support boat, and it can only just keep up in a F4/5 mid channel. Nothing smaller would be suitable for us.
I'd be pleased to help and give advise if you're up to anything similar.