Attached is a little info on the fastest Windows 7 Pro 64-bit xw6600 I have built, and some tips on how to duplicate that if you wish. One can boost the video scores to 7.8/7.8 by using a nVidia GTX 650 Ti Boost dual slot card, but the single slot Quadro 2000D is fine for our medical workstation needs, draws less power, and is very quiet. The "C" boot drive is a 160GB Intel X25-M Generation 2 (34 nm fab..... don't get the older G1 50 nm version). A nice alternative is an Intel 320 SSD, which has larger sizes available and also works perfectly in these SATA generation 2 workstations. The "D" storage drive is a 1TB Western Digital Red. I've posted here previously on how I used DBAN to allow that to work with the xw workstations.
This build has USB 3.0 added in to it, via a HP TI 2x2 PCIe card originally produced as an option for the Z600. That is handy..... two front and two rear USB 3.0 ports available, and it uses the same TI chip that is soldered onto the motherboards of the more recent Z workstations, and thus uses the same drivers. I do a little tuning on the chipset/memory/front case fans, and the xw6600 runs nearly silent, and cool.
All of the xw6400 processor upgrade information and techniques posted here work with the xw6600 equally well, but a different family of Xeon processors is used, as you can see from the QuickSpecs attached. The fastest quad core HP ever certified for this workstation is the E5450, and the latest sSpec code version for that is SLBBM ("E0" stepping.... "C0" is the older stepping and that has sSpec code SLANQ). Always buy the newer SLBBM version if you have a choice, because that will have improvements built into it by Intel. Two of those E5450s are running in this xw6600, courtesy of eBay.
Not bad... the maximum score possible for each category of the built-in W7 Windows Experience Index speed testing software is 7.9: