I really like the potential of Varishocks as reliable stock mount adjustable dampers, however I haven't found much feedback on their adequacy at the track.

IIRC I've seen D. Pozzi mention that he's had reasonable "on track" success with QA1 adjustables. Given that Varishocks are higher quality they may be the ticket.

As far as I can tell, Penske and Bilstein adjustable shocks are not available in stock mount configurations, but it could be possible to have them custom made ($$$).

Bilstein (mono tube non-adjustable) dampers appear tried an true and can be re-valved at the factory but there is a min three week turn around (not such a good option for trial and error tuning). An option could be to get two sets to buffer the revalving turn around time. Two sets plus revalving fees would quickly add up to the cost of Varishocks.

If Varishocks' track viability equals that of Bilstein monotubes then ultimately Varishocks would be the better value.