You are talking about 2 quite heavy cats which may be difficult to right. If you want the lightness of an A Class (almost) with a spinnaker, check out the Spitfire's small relation, the Shadow at: www.swell-catamarans.co.uk
In a Club race last Sunday it beat a Tiger and a Hawk around the course (as well as the usual Dart 18s and 16s)- without using its spinnaker.
Dermot.