Where's Mimi Some great articles about width and performance out there. Not sure how geeked out you want to get but here is just one of many articles in Bicycle Quarterly
In racing, a skinnier tire will come off the line faster, however, once up to speed a wider tire has no less performance and will roll just as fast. I am not a racer but have often caught up with a pack of roadie's and been able to ride with them on our local "bikeway" on my touring bike with my 650b x 40's. Going from a 23 to a 28 isn't going to drop your performance and hopefully will make your ride way more fun as you won't be bounced all over the place.