slick ??? for you guys

im in need of new slicks and plan to buy some here soon if it stop raining and i can see getting back to work. but anyway how much diff. have you guys seen going from old tired slicks to new slicks on the same set up.... right now i have 28/10.5 m/t but plan to step up to a 29/10 and a gear change from 4.57 to 5.13 ....jsut looking for info from old to new as i know the gear change will be a test....