1) On a 32bit windows box, 3gb to 4gb are always reserved for memory mapping. Therefore, a windows box with 3gb and one with 4gb will both still have only 3gb available to the OS. I believe this limitation is imposed by the BIOS.

2) The Xeon MP does not scale very well running most types of application, even the latest XeonMP's have a shared 400mhz FSB (3.2gb/s of bandwidth) - Intel have tried to improve scalability by increasing the L3 cache size, the latest Xeon Mp's have upto 4mb of cache. The Xeon 800 has an FSB of 133mhz (1.06gb/s), sharing this bus between 8 processors is like trying to suck a bucket of water through a straw! (scuse the analogy). Remember also that all I/O goes through the FSB, a 15k SCSI drive or a single gigabit ethernet LAN is capable of bursting at 80mb/s (8% of your FSB bandwidth!).

3) Also windows does not scale well at this level, try running this on an OS that really scales (solaris, some linux, AIX etc).