The larger 1MB cache of a Celeron M is highly preferable and I've found a 1.5ghz for ~$90. The firewall is database driven so the larger cache would chew right thru it.
Also, is there any physical difference between the uFCPGA478 and Socket 478?
TYAN S3098G2N-G Socket 478 Intel 845GV Flex ATX Motherboard
http://www.newegg.com/Product/Product.a ... 6819112209




