Linux driver 331 gives 10-fold performance degradation with Quadro 410

Drivers up to 319 perform well with Xorg consuming 0-5% CPU, but with 331 or 340 or 346 the performance is very bad with CPU usage of 30-100%. However the performance problem occurs when using Quadro 410 but not when using Quadro 400.
The application is 8-bit showing a map using tiled layer graphics to include text and graphical information. The graphics are very simple (mostly single colour outlines) and the colours are mostly solid. Modifying the application for 24-bit colour makes no difference to the performance.
The PC is an HP Z420 with 2 x Quadro 410 (or 2 x Quadro 400) and the operating system is CentOS 5.6.

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