Nvidia has transitioned their entire product line, including high-end, to 55nm. They have access to the same process technology as AMD for GPUs, as both companies rely mainly on TSMC for their chips. In the past, Nvidia has been reluctant to move to a new process with a new architecture (similar to Intel's tick-tock strategy), however, they've recently made it clear they're no longer willing to lose the process war against AMD, especially when they place more orders with TSMC. There were a few news bits about this causing friction with TSMC, as I'm sure TSMC was glad to have their older processes heavily utilized by chip orders placed by Nvidia.