The 160GB model will arrive in Europe in October, for 299 Euros, according to our man on the ground at Gamescom. It will replace the 120GB model as the standard. The 320GB version will be available September 15, as part of a Move bundle, for 349 Euros.
Update: Sony announced a North American release for both of these systems on the PlayStation Blog. The 160GB is shipping to retail now for $300, and the 320GB Move bundle, with Sports Champions, a Move controller, a PlayStation Eye, and a demo disc, will be out September 19 for $400.
