Shoes levels

Who can tell me how much each level in the sports shop items increase your player stats ? I ask this cause teams 4 levels below have players at their top level 325, where as mine is 345, yet they out run mine as if mine are running in toffee ?
Team strat, player strat, player stamina, player d speed all factors
items add 5, 10 or 15% to your skill, so someone with speed of 325 with lvl 3 shoes has an equivalent speed of 373.75, and all the factors BM mentioned influence it too
Shoe is 15 points, not percent
like MB said its 15 points not percent
Carshalton lied to me then
That's training not shoes