what is the largest mah 25c single cell battery available? also if there is one higher than 4000mah... will it be legal for the sportsman class? the rule states 25c but no mah limit.

The only single cell 25C lipo currently approved by ROAR (and ROAR approval is needed to be legal for events and tracks following the TOUR rules) is the 4000 MAHR SMC pack. While it is possible that a manufacturer may have another 25C pack currently going through ROAR approval, it is unlikely since the manufacturers all seem to be chasing after the highest possible C rating.

Here is a link to the ROAR LIPO battery approval page. It will tell you what is currently approved but not what has been submitted for approval. For that you need the rumor mill.

http://www.roarracing.com/approvals/lipobattery.php