1) I meant : could you try to turn on the Aiming Preview and see if it creates a similar lag ?
2) Yes, Microsoft authorized me to raise it to 2GB, but this will delete everything on it, so people will have to download their Mods again ; so before doing that I'd like to warn all the users by posting a message in the TE4 Xbox Club, but I'm still waiting for Microsoft to activate it...

By any chance, can you see the club on the TE4 page on your Xbox ?