I am a normal end-user of workstation, just treating it as a normal desktop for my usage. I own both Hp Xw4400 and Xw4600, yes I know is kinda old (LGA775 era) and don't make relevant sense in today's standard, so I will just share my experiences. I own it because both unit were discarded by some rich fool, so I just took it back home. Only thing that I dislike was the fan noise, it was very loud if I am using it in my room without AC, fan speed only reduce if it detect ambient air temperature drop. Other than that I would say the motherboard were built tough, after 10+ years it still runs great. Although there were 3 x bad capacitors on the Xw4400, but it still continue to runs and I already replaced them. Another thing is a plus for HP is ability to support ECC and non-ECC ram, if i not mistaken, compared to dell precision, HP allow user to either choose ECC or non-ECC. Which is good, cause ECC memory upgrade was a hassle because must match pair this and that... 

Xw4400 (C2D e6300, 2GB ECC, 160gb HDD, Nvidia 9400GT 1Gb)
Xw4600 (C2D e6850, 2GB ECC, 2 x 80GB WD raptor, Quadro FX4600) - I estimate this unit to cost at least RM10k

Now both unit i retired already cause i already got a i5 desktop, and still keeping both for collection.