Not sure what the usage is but one of the reasons to upgrade is to get antivirus. Can't imagine that the hardware that was used for a 5.6 install is going to perform clam antivirus scan very well. My P3 866 with 384 Mb ram takes 100 minutes to do 8 Gb. There are some other posts detailing long scan times. There are probably other issues related to old/obsolete hardware that I am unaware of.
Then if you are getting better hardware you can set everything up and just copy over what you need...