You got to think do you want solid or deep bass? Most 8's sound solid with the seats up and while a 10 hits harder or more deep then a 8, usually you're going to have to place the seats down to get the 10's to sound their best (at least seams to be the norm with non solo baric woofers, look as some of the posts...some members have taken out their 10's because of this). Two non solo baric 8's seem to sound better in the trac then a single 10 non baric. If you do two solo barics 8's, well they pretty much will out thump most dual 10's that are not solo barics and give a single 10 solo baric a run for it's money if you get the box spec/air requirments down for dual 8 barics. It's a up to you if you want seats up or down and how much thump you want.