Anything more than 245's, and a fender roll might be needed. I've 'seen' 265's back there on cars with drops w/o fender rolls, it can really depend on the brand of tire, and it's physical qualities (is it 'rounded' or 'squared', etc..) Anything bigger than 245's, and a fender roll gets more and more into the picture, especially since you do have the sports package and are already riding a little lower than the non-sports suspension cars.
Everyone has opinions about their tires, I'd say goto tirerack.com, pick the 5 tires that most appeal to you, and compare them (Tirerack has a good amount of feedback on every one of their tires, so you can read what others have to say, and also compare their ratings for the tires including how they do in wet weather, which is what you're looking for).
On that note, I'd pitch getting Pirelli Pzero Nero M&S's for an excellent all-season tire that does great in the rain. It gets some of the best ratings at tirerack across the board. Make sure to include them when you do the compares on tire rack, you'll see what I mean.
www.tirerack.com