Hi All, I'm debating getting this laptop case from REI for my 13 inch MB: http://www.rei.com/product/776240 It has everything I want, it's like a sleeve but has a handle and a possible strap. The problem is that the small is for 12 inch and the medium is for 15 inch. Does anybody think it'll be a big problem if I use the 15inch? My MB will slide around a bit in it but I just don't know how much I should worry about it.... Also, if you know of a similar case for a 13 please let me know Thanks!!