As others have said, changing to a 28 in the rear isn't going to provide you with much relief. My bike has a compact crank (50, 34) and a 12-32 cogset in the rear. The lowest gear is more than sufficient to allow me to get up any of the nasty hills here in the Texas "hill country". In my experience with mountain bikes and road bikes, a low gear ratio of about 1-to-1 (e.g., 34 chainring to 32 cog) is low enough to get me up any incline.