I just figure well recorded and produced discs work just fine for me to tune too. I'd rather go to my local CD resale store and find me some good old classic albums. But, try that Sheffield disc, it well probably do it for you just fine.
I needed a good mono track to tune my new HU. I had read on other forums that this CD had one that worked well for the auto tune feature on my p99rs. I think the tracks that are purposely distorted are neat to see what level of THD I can notice. Other than that I probably won't even play the others...