What size library is itunes scaled to handle? As I built my library from 75gb to roughly 425gb (had to move my itunes library to an external hard drive - firewire connection) i notice significant lagging while scrolling, while clicking on a song to play... for pretty much everything. I've turned off genius, auto-update, i've simplified the file-paths (decreasing them by roughly 30% after final addition - itunes creates file paths by artists name). I've then cleaned my hard-drive, registries, and reinstalled the operating system - updating all programs to current levels. Throughout this I monitored my usage on iStat menus. While overall processing speed improved i tunes continued to lag. Can anyone please provide some details and or a prescription for relief from these lagging issues?