My guess is that currently 40% of all Cypress wafers being run are being binned entirely as Cypress LE in order to meet demand. This is in addition to those wafers being binned out normally. Cypress probably bins out far more Cypress Pro parts than Cypress LE parts, while demand is mostly for Cypress LE. If Barts XT is, as stated, it will be relatively low yield. In fact, the number of Barts XT GPUs yielded per wafer will probably be less than the number of Cypress Pro GPUs yielded per wafer in spite of Barts yielding up to 40% more GPUs total than Cypress.
With the introduction of Barts, AMD will want to halt all Cypress production done purely to meet Cypress LE demand. But low yields of Barts XT will mean lots of Cypress Pro GPUs will need to be produced to supplement demand for Barts XT. And there will be some residual Cypress LE GPUs salvaged from this producion.
Barts XT should be intermediate in performance between Cypress Pro and Cypress XT, and will probably be introduced at $249. Barts Pro will probably be introduced at $179. Cypress Pro will drop to $219, and the Cypress LE GPUs that are true salvage from Cypress Pro production will go head to head with GF104 768. After introduction, Barts Pro will float above the price of Cypress LE just close enough to keep Cypress LE demand in check. Cypress XT will probably drop to $329.
Turks XT should be intermediate in performance between Juniper Pro and Juniper XT. Turks XT will be the new RV740, and then some. In DX9/10 it will range from RV740 to Juniper Pro+ level performance, and in DX11 it will be closer to Juniper XT level performance than Juniper Pro level performance. It will, like RV740, be introduced at $99, with Turks Pro being priced at $79. Best of all, Turks XT will be under the 75 watts TDP power limit of the PCIe slot. While Turks XT will, in general, not perform quite as well as Juniper XT, ATI will EOL Juniper after Turks is introduced.
There will be a significant price gap between the under $100 GTS 450/Turks XT and the GTX 460 768/Radeon HD 5830 but since this gap will be duplicated in both the AMD and nVidia lines, it won't really mater. If nVidia introduces a further cut down GF104 to fill this void, AMD can respond in kind. Even if nVidia doesn't introduce a SKU to fill this void, AMD will eventually fill it with a 28nm GPU series that is 75% of Barts.