Ditto the above, namely bumps and smoothing issues. Randym makes a good point - as time goes on it becomes more likely that the people still using P4 are probably power-user/purist/die-hards who are big and ugly enough to tweak a made-for-P6 product, with utilities to convert to rsr etc. As a merchant I will be focussing on P6 product with perhaps something in the readme to help P4 users get things to work. Eventually P6-only will allow lower poly models because they don't need extensive beveling, vert splitting etc to prevent P4 over-smoothing. Ooops, rambling in a survey, and it didn't say "use extra sheets if necessary" :o)