I don't have any facts but I would bet that the bike would be to lean for comfort if we remove both without a tuning device. As of right now I can not find anyone offering a tuner for the 2013 yet. For the best performance I think we need to remove the cat, add free flowing muffler, and remove factory airbox and install the Kewl Metal high flow intake system. With the 50lbs of weight reduction and the more air in and more air out we should be able to get some good gains! After that there isn't anything else let on the aftermarket to improve performance. You would think that after 6 years we would have cam options, big bore kits, and several high flow intake options with cool air intake ducting to foglight holes.
I don't know how you would find it, but back in '09 or '10 there was a big bore kit available for the 990.