Nippon Challenge is good and the 2x 15 min races are my preferred format.
When it first launched we had some big bhp cars run and granade at the same speed, in the second year they capped the bhp to 300, current talks are ongoing regarding what regs for next year and the upping of bhp if there are interested cars.
CSCC won't be bhp limited.
perhaps its my age but I am knackered at the end of a 40 min race, I am only tempted to do the longer races so I can get to race at Oulton and Anglesey again.
i plan to do the full Nippon season again next year, the class breaks are based on engine bhp and min weight, I will be running in GT300 ( upto 300 at the flywheel and min weight of 1110kg, post race inc driver). There is talk of the classes changing to be engine capacity based, with 1.7 multiplyer for forced induction for 2013.
another option is the BRSCC Eurosaloons, 2 x 15 min races, I don't think there are any limits