start by reading this TR.
The ext_cache_obj can be monitored using the stats command, or using PerfAdvisor. In PerfAdvisor its not enabled by default so you have to add its object and associated counters. then you can use the same basic analyis used in PCS with the actual FlashCache card.
I hope that makes sense.
basically you are going to look at the same counters defined in the TR, but you are looking at a real card not a simulated card.