My experience from 6 years racing the PIK agrees with Bill's. Sand
with 600 at 45 degrees back to high point of airfoil. Clean with water
with generous helping of dish soap. Wipe dry, don't rinse.
Other very important factor in climb of PIK is flap setting. It wants
to fly at a constant AOA with additional lift for tighter turns added
by flap setting. As I recall, I used 6 deg for 30 deg of bank, 8 deg at
45 and changes flap setting whenever bank changed, even recentering. A
lot of work, but it did help performance.
Good Luck UH