I already have some data w.r.t P55 (Gigabyte UD4P/UD6/UD7) SATA2 (Spinpoint F3) and WD SATA3 HDDs (WD1002FAEX) but am waiting for new P67 boards so that I could build them in this fashion:
Crucial RealSSD C300 SSD - 256GB - 1 No per machine
WD Black 2TB SATA3, cache 64MB (WD2002FAEX) - 2 No. per machine
I will initially build 3 machines but with different MOBOs (once I get them replaced):
Gigabyte GA-P67A-UD7 (2600K)
Asus P8P67 WS Revolution (2600K)
Intel DP67BG Extreme series (2600; most importantly for Vt-d).
Then I could really dwell into P55/P67 SATA3 performance (SDD vs HDD) in depth with real time loads.
To my understanding, SATA3 HDD aren't so promising compared to SDD in terms of touching anywhere near to the theoretical speeds, be it P55 or P67 platform. Whereas USB3.0 has shown much better results in P55 and I expect this to improve further in P67. But note that Gigabyte MOBOs have superior USB3.0 speeds compared to their Asus counterparts. That's all for now.