I contacted two of the Russian queen suppliers on their recommendations on treating Russian for varroa before winter.
Coy's Honey Farms recommended treating for varroa if above the 5% infestation level. Coy is the current President of the Russian Bee Breeders Association. Unfortunately I don't know what 5% infestation means or how to test for it.
Foley's recommended treating if ANY sign of varroa is present. He stated that up to now he had never treated Russians for varroa, but mentioned that hive losses during last winter has made him want to err on the side of caution. Foley's is located in Iowa and had similar winter conditions as ours.
This seems to indicate a little backsliding on the excellent varroa resistance to which the Primorsky Russians have been attributed. Think I will treat all my Russian hives with a 1/2 dose of formic acid (MAQS) as a precaution.