Tektronix recommends immersion gold surface plating for all P68xx probes. Some customers have experienced success with immersion Silver and HASL surface finishes for the P68xx series probes.
While we continue to recommend immersion Gold as the best surface finish, we believe you will see similar results when using OSP as with HASL. Further, we saw evidence of increased resistance as the number of cycles increased on the OSP tests. Environmental conditions will affect results as well - as temperature and humidity increase your results will decrease.