I believe that Kev's mods will not in themselves give any 'performance' gains but will 'correct' a few issues in the running that seem to affect these bikes.

His advice is all here..positive gains in the running can be made by changing the stock filters for ones that allow more air flow.Namely DNA ones. These in combination with a less restrictive/freer flowing exhaust will give you performance gains.

At least thats what I understand.HTH.