We use those Z820s with Win 7.1 at my work. Windows 8 is the biggest joke since Vista! Nobody in any 9-5 business is booting Win 8.Honestly, I should shut up now and walk away, but I cannot. The only real problem I see with what you are saying here is that I will have to use windows 8. Now if YOU tell me I can use the HP Z820 with 24 cores and have a lot more ram, and put Mavericks on it you might have me sold.
But to be fair, the Z820 is almost 10 times bugger than the mini-pro.