Stupid question - I took part in a few Cat 4 races this year and am still very green & learning the ropes.
I noticed a lot of other riders had deep-set carbon wheels on their race bikes and I would have been in the minority with none. My wheels are I though good- carbon clincher wheels .
For the majority of riders using them, carbon bike wheels merely have a placebo effect, particularly judging the number of folks tooling-around sportives with carbon wheels going at 16mph in the vain hope that it will make them faster.
The other thing to bear in mind for Cat 4 racing is that carbon is not that resistant to impact damage. http://www.carbonbicycleonline.com Eurus are good, reliable dependable wheels perfectly suited to club racing.