The FOG Configuration->FOG Settings->FOG_PIGZ_COMP is defaulted to 9 which means maximum compression/slowest upload.
It only functions on the upload process.

If this is where you’re trying to “speedup” the images, I’d recommend adjusting this value.

If you’re trying to “speedup” the download of images, then check your networking. Is there 10/100MB limiting that lab down from a gigabit network?

the hosts that are looking for the old IP will not communicate with the server while it’s running unless you reconfigure the hosts to look for the new name or IP. assuming you set up your dhcp server correctly for the new IP of the server, network boot operations should be unaffected. you could probably make a snapin to deploy to all hosts before changing the server that updates the config files on the hosts for the new server.