If you have enough room, it's always better to play it from the harddrive.
I've never had slow loading problems... then again, I've been playing it from my xbox for ever since I can remember... But, I can see how it would take longer to load... It has to load all of the necessary files into the caches on the drive, and then it has to read the override files directly off the disc. That can take awhile.. especially if you've got skins or alot of gffs
before you burn a disc with the .ini, test it to see if it'll load from a custom override directory.