If I had my 'druthers on a "do it all" boat, I would have toons equipped with lifting strakes for sure, conventional 2 tube or w/center. If you think you might need a center tube, you're likely going to want to order up some extra power - to maybe 150hp. You can easily get away without it with a 90, but when you get up over 115 or so, you're going to have to figure another expensive option, which is hydraulic steering. Goin fast aint cheap!
After being converted a couple of seasons ago, I am now a dyed in the wool 4 stroke convert. That is THE way to go for pontoon boats!