fritz, it looks like many of the pyramid machines _are_ supermicro (what else), you will find supermicro systems in many OEM products ...
i personally don't use dell because they don't provide sufficient information about the used motherboards and i don't like surprises too much.
regarding 2) i mentioned 4-core CPUs (along with intel 5000 chipsets) don't add the awaited performance increase compared with 2-core CPUs, but clearly a 4-core system (2 proc x 2 cores) is more performant than a 2-core system (1 proc x 2 cores)
for sampling only 2 x 2,66 GHz XEON should be already sufficient, even with 16 or more GB RAM - how much the harddisks will turn up as bottleneck with 40 or more instances has still to be found out (chipset, drivers, configuration, harddisk model, raid modus adds to the overall performance).
SAS and SCSI (up to 15.000 rpm) is really expensive, flash not yet available with the needed capacity, so sATA II looks like the preferred choice, again raptors are more expensive than 7.200 rpm drives but add significant performance (eg. average seektime is 4,5 ms whereas normally it is about 8.5)
christian
and remember: only a CRAY can run an endless loop in just three seconds.