R420 - set to ship as the Radeon X800 Pro - is pitched directly at the 6800 and according to a report at Hard OCP, will offer comparable specs.
So just like the 6800 Ultra, the X800 Pro will be fabbed at 130nm. It will support GDDR 3 memory across a 256-bit bus clocked to 1GHz. It to is priced at around $399 and will initially appear in AGP 8x boards. The X800 Pro's core is clocked to 500MHz.
Unlike the Ultra, the X800 Pro contains 12 rather than 16 pixel pipelines. However, its big brother, the Radeon X800 XT, due to chip on 31 May, according to the report, will feature 16 pixel pipelines, along with a core clocked at 600MHz and memory running at 1.2GHz.
Both Pro and XT parts are based on the R420. On 14 June, the report reckons, ATI will ship a variant, the R423, as the Radeon X880 XT. It's a PCI Express-native part specced to match the 800 XT and like it retailing for around $499.
In the same timeframe, ATI will release the R420-based X800 SE, a lower end part clocked at 450MHz and with only eight pixel pipelines enabled. The memory bandwidth is halved too, with the bus set at 128 bits wide. It will use regular DDR SDRAM, and only 128MB of it, compared to the 512MB limit of the other three R42x chips.
Hard OCP notes that its source this time round isn't within ATI, but one "that has proven to be correct in the past". The information matches that quoted recently by AnandTech. ®