"pros" dont even run modded mills. look at the worlds. standard vspec with the new lightweight cooling head.

and also 1,2,3 at the US nats on standard vspecs

the only time when pro drivers do run something different to whats avaliable in the shops, is mainly for research and development work.

Also when you say modded mills, there are two types.

1. is where the mill is modded by factory. e.g Rody Modded C5's and JP modded B5N's. In this case usually there is more than just doing some sleeve and crank work. On factory modded mills, you may get extras like ceramic bearings, better rod, hardened crankcase and crank, better quality seals and carby etc etc.

2. then there are engines that are modded by backyard operators. I would stay away from them.

If you do go for a "modded" mill, go for a factory modded mill as there is more to a mod than just taking the sleeve to a dremel, factory mods also make it last longer and hold a tune better. Also thier sleeve work is all done accuratly to the micro millimeter with cnc machining.