I've added sponsons to a 92XP before. I missed it on my first guess and it plowed through the water terribly. I had to raise them up so the ski didn't feel like it was towing another one. Of coarse that meant I had 6 drilled holes to fill under the waterline.
My 90 has those big sponsons from an early GTX's and it handles great. I think it's worth doing if you can nail it the first time and avoid extra holes.