My Dell 8400's P4 520 CPU just died after a power failure. It's been such a champ all of these years, that I'm going to just replace the CPU. I've read somewhere on the Dell forums that the mobo can use all 5xx and 6x0 CPU's but the 6x0 series are 64-bit, and the current CPU is 32-bit. Is there anything keeping me from upgrading to a 620? If so, are there any other lg755 chips I could upgrade to?