Well, 90% of beachballs happen when CPU has to wait for HD...
Majority of people don't need i5, but they still want one
Hate to break the bad news, but CPUs wait for HDD IO 99.999% (or more) of the time.
Im bettin the beachball thing...aint waiting for drive IO.
Im not a software expert, and with that analysis, Id bet you aren't either.
But I am a qualified enterprise storage performance expert, and speeds & feeds on the outside of the box only impress people that dont know how things really work.
As earlier stated, interface speeds only start to matter in larger shared infrastructures where intelligent IO not present in desktop/consumer designs makes it more advantageous. Any amount of random IO destroys the idea of a spinning media drive saturating SATA-2 speeds in a real world workload.
Apply a little queuing theory, then plug in what you can find about bus interrupt, drive rotational and track-to-track latency numbers within SATA, and you'll find a lot of empty bandwidth in the path.
It can take a significant number of FCAL/SAS HDD's to saturate a 4Gpbs FCAL loop with reasonably normal real-world IO data rates and patterns out 'in the world' as well.
But it all comes down to defining the unique dataset, and the unique workload to be applied against it. Is it realistic..benchmark, or synthetic to prove a point?
I'd bet, that if someone had a specific dataset, with a specific workload, that had specific IO requirements, wouldn't be relying on internal storage to get the job done anyhow...also earlier stated.