The Hollywood Reporter are...reporting that, according to a "major retailer", Microsoft will indeed be slashing the price of its Premium 360 bundle next month by $50, from $349 to $299 (no specific mention of the Arcade of Elite). They also say the cut will come into effect before E3, which takes place in a couple of weeks. If anyone's wondering as to the reliability of this "major retailer", it's worth noting that the Hollywood Reporter nailed the timing and details of the last price cut, which took place in August 2007. It's a safe bet these are the same sources.
Microsoft slashing price of Xbox 360 model [Hollywood Reporter]