Following the advice given, I have decided to go for a high-end desktop configuration with the ability to OC the Q6600 CPU as the G0 model of this CPU has some excellent OC potential, which is something I have always wanted to look at. HW configuration as follows (ESXi Whitebox HCL confirmed):
ASUS P5Q Deluxe
CIT 550w Gold 12cm Silent PSU
Intel Q6600
Artic Cooling Freezer 7 Pro Rev 2.0
Geil GX24GB8500C5UDC DDR2 1066 4096MB x 2 (Kits of 2)
Zalman Z7 Plus ATX Mid Tower Case
ASUS HD 4350 PCI-E 1GB DDR (remember this is a ESXi whitebox so GPU not a key area).
Intel Pro 1000 GT PCI Card
Samsung 8GB MLC SSD SATA (for the ESXi install)
WD Caviar Blue 500GB SATA 11 16MB Cache x 2
HL DT-ST DVD RAM GH22NP20