Arrgghhhh the slowdown is so bad I might need to send it back.
Surely the fact that a full wipe to factory settings temporarily fixes it shows it is a software issue?
I would try out CM10 or paranoid android first. The only real advantage that this modaco rom has are the "extras" not really the rom itself if it wasn't for all the packaged hacked apps it wouldn't get a look in. I was getting mega slow down and switched over to paranoid android 2.1 and a custom kernel and it fixed everything and added loads of great stuff.