Have no idea what they are talking about, but guessing they had it on a SATA II port (3GB) or didn't have the proper drivers on the mobo, might even have been a SATA 2 cable - regardless SATA III is rated up to 6GB/s and the Samsung 840 Pro is rated (by Samsung) to run up to 540 MB/s read and 520 MB/s write - which is far far away from 6GB/s, as mentioned there's no single drive that can fill that pipeline
Originally, I threw a Hyper 212 EVO on this , which started getting warm (for me) at about 4.3, was idling at about 41, but I had a CM GTS v-8 on pre-order, they were finally released on the 13th, got it last Fri, now idle is down to 31, expect about 27-28 once the AS5 is fully cured, have it at 4.6 now and load is in the high 50s