It seems that a new product indeed is inbound as prices in EU pricewatches show a drop the sales price of the GeForce GTX 580.
The GF110-based GeForce GTX 580 now starts at roughly 339 EUR if you look at Geizhals.at. Interestingly enough the new price makes GeForce GTX 580 1.5 GB a little cheaper than the Radeon HD 7950.