The prepare_cached method prevents the statement handle from being created more than once (in a persistent environment like mod_perl), but that's all it does. The query still has to be executed by the database. It should be faster to pull the data from a cache.

Maybe you're getting ahead of yourself here. Is the site slow now? Have you profiled it to find out where the bottlenecks are? It could be that this particular query runs so fast that it's not worth caching.