For concrete, Pro-line S3's (any) will give you maximum traction.
I just finished running a race on concrete and the tire to have was Take-Off's 27-CS with a medium T-O insert or the premounted.
The Pro-lines S3's are a little soft so you need to use a firmer insert. HPI 26mm pro molded inserts work good on all of the S3's except the Road Rage tread. For the RR tread you need a flatter insert like a Yokomo 26mm because the rubber is thicker on that one tire and will cause it to be too rounded.
Did this make any sense?
I would try the Take-Off's first, if you can find them. Everyone claims they work great. (I am going to try some this weekend)
Hope all of this helps, good luck racing.