Do not buy w580. I am using it right now. It has been just over 4 months and i have already got its battery, upper keypad and lower keypad replaced. There was some problem with the keys of w580. The keys used to crack easily although now i think the company is manufacturing more durable keypads.
^^E6 has DOS emulator and VLC, two things you can never find in w850. There are many more similar apps for the E6, but it will be outdated soon, by september, as developers for linux mobile will shift focus from these highly fragmented mobile linuxes to Google Android. So Palm Linux, Familiar Linux, Pocket Linux and Motorolla Linux mobile users better watch out. There might be a shortage, or atleast a state of negligence, of new programs for your mobiles.
PS: Its only my personal view, and is highly propable because of hyprocracy in our market.