Nvidia has either suffered a catastrophic breakdown or the firm is suffering from shame. Normally a 'new' product like the 256MB version of the PCI-E 6600GT would lead to fanfares and an inbox full of press releases. But everything has been done in a very hush-hush way.
It might seem strange that nVidia has had to sneak the 256MB 6600GT out but it's one of the firm's darkest secrets. It can't have escaped the notice of many gaming and graphics fans that you could buy a 256MB AGP version of the chip but were completely out of luck if you tried to get a PCI-E version. And the reason was bordering on scandalous.
When the 6600GT launched, the game that everyone wanted to run was Doom 3. It gave all the nVidia fanboys warm feelings because the game ran beautifully on their hardware and badly on ATI chips. But that's not the whole story.
It didn't take long for nVidia to realise that two 256MB 6600GTs in SLI could give the 6800 Ultra a run for its money in Doom 3. And two 256MB 6600GTs cost about 30% less at the time. The solution was simple: kill the 256MB version and only sell a 128MB version. That way the cards were hobbled and couldn't interfere with sales of the top end Ultra. Seems a bit underhanded of Nvidia, in my opinion.
Now that the 6800 has been killed off there's no problem having a 256MB 6600GT back on the market. A pair in SLI shouldn't interfere too badly with sales of the recently announced 6800GS or with the upcoming 7600.
Source