Where power is limited, such as on the Enstrom F28A on a hot afternoon washing and drying the MRB/TRB will give approx 1 inch of power over that of a filthly one.

Performance has been assessed for your flight Manual graphs using clean blades(main and tail rotor), so it should not take a brain surgeon to work out the fact that if you have to use the graph to assertain your performance then the blades MUST be clean.
Using WD40 or similar will be the catylist for dirt to stick, therefore clean, dry and polished with a thin layer of an approved polish is the best you can do.

Hovering above flowering grass will produce a layer of pollen and dirt that sticks better than araldite or dried hydraulic fluid.

Going off on another thread;-

In summer I clean the front of the helicopter, then spray with furniture polish, but do not remove the film of polish and the flies literally fly off. Do the same on the front of my car. Just wipe off the dust and the odd fly and spray again. Saves hours of hard work.