Pyro, I have no idea what you are talking about needing multiple licenses for a dual processor. I have several xw6200 and xw6400 and all you need is a single Windows 7 of any version. I have Windows 7 running on both Dual and Quad processors with no issues.
Matt I know this is a year old, but you are correct, these machines are rock solid and quite powerful which is why I continue to use them. I have 8 gig Ram on all of them except 1 on the xw6400 where I have 12 gig and use it as a video editing machine CS5, of course upgraded with a 500$ GEFORCE video card.
The xw6200 continues to perform excellent. I have qty4 23" monitors using two dual port FX3400 cards. One was the original card and the other I purchased on ebay for 10$. I use this machine for stock trading using all 4 monitors and have zero issues using Windows 7 64 bit
I also have in this unit qty of Three 3T SATA drives. One drive is used to backup my network to, and the other two drives are used as backups for our video production files, a very inexpensive and quick way to back up data.
On one of the other xw6200 we have a full suite of graphics software and web development software that is used extensively.
The xw6200 perform excellent, however for intensive applications such as video editing or if you want to use hard drives in excess of 1T then you will want to migrate to the 6400s. We only purchase the xw6400s now.
That all being said, there is incredible performance gains to go to the new processors and as such we just upgraded our main video editing system to a new system that is using the Haswel i7 4790-k processor and GTX motherboard. Now our export to video only takes 3 minutes where before it took approx 12 minutes on the xw6400, and all production is absolutely flawless with no hickups.
So.....bottom line, if your on a budget you will find that both the 6200 and 6400 are excellent even in 2014 for nearly all computing needs. I have personally never had such a stable computing environment, with nearly zero glitches and no hardware down time. Love HP!!!