According to the drawings that our colleagues from hardware-aktuell.com managed to get, both new ATI cards are going to be 23cm, or 9-inches long.
As we wrote before, the HD 4870, or the RV770XT will have a fatter dual slot cooler while the RV770Pro will have a single slot cooler, similar to the previus HD 3850 card. ATI's cards will end up few centimeters shorter than Nvidia's GTX 260 and 280 which will be 27cm long, at least according to some first rumors.
The 27cm length is well known, as this was the length of both 9800GTX and GX2 cards. Of course, you must bear in mind that performance-wise Nvidia's GTX 280, 260 and HD 4870, HD 4850 are just not in the same league.
You can check out the drawings here.
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ATI's new cards are 23cm long
Both HD 4850 and HD 4870