Don't be afraid of a bit of crew weight. The Stealth should be able to take the same weight as the Spitfire. I normally sail with a lightweight girl crew. But I sailed a few events last season with a 70k to 75k crew. We won an event in force 4 to 5 winds, beating Hurricane 5.9 SX and other spinnaker Hurries, even on the water, and came 2nd in another event in light winds against Huricane 5.9 SX, Tigers and Spitfires.
I raced against a singlehanded Stealth a few years ago ( http://www.catamaran.ie/Results/2002/InlandResult.htm ) and while his boat speed was faster a lot of the time, I beat him on the water in 2 out of the 3 races. He lost it on the turns, hoisting and dropping his spinnaker.

Enjoy your Stealth,

Dermot.