I have a Samsung 250 gig. I turned on the Rapid Mode. I didn't see any difference in performance on my PC. The only difference I saw was increase in benchmark scores. I turned it off because of the other things it did to my system. It was using almost 2 Gigs of my memory. It turned on Hibernate, and Indexing service, which I had turned off. It changed my Virtual memory setting and my Power options, all of which I didn't like. The first pic is WD Black 1TD HD that I had original . The second is SSD with out Rapid. The third is SSD With Rapid.
By the way your WD Black is running nicely!