I think my Hyper-V server is finally behaving itself. In searching for a resolution to the intermittent BSOD, I finally found something that seemed to match my particular combination of hardware and software. I've installed the hotfix for Windows Server 2008 R2 that works around this "erratum" in Intel's Core i7 processors, and so far so good.
The other reason Hyper-V has to be happy is that I also purchased a proper case to house the hardware in. I ended up getting an Antec Three Hundred case from MATS Systems. It's a nice, smart, functional case. While there are cheaper cases around, Mark from MATS recommended the Antec models in particular because of their cooling ability. The Three Hundred (the model, not the price!) comes with two fans, and has decent capacity for mounting a few hard disks too.
Let's see what a difference a proper case with extra fans makes:
|Component||°C (DIY Case)||°C (Antec Case)|
|CPU Core #0||41||32|
|CPU Core #1||36||29|
|CPU Core #2||43||34|
|CPU Core #3||38||28|
|HDD ST314003 #1||53||36|
|HDD ST314003 #2||55||35|
That's quite a significant drop. Those temperatures seem much more reasonable too.