does second gpu for display improves performance? computing - display

I currently have a gtx 460 on ubuntu 11.10 - toolkit 4.1.
How necessary is to have one gpu for display and one for computing? Will there be significant performance improvement in kernel executions if I add a second gpu for display? I know that many things depend on application and coding but I believe that in this matter there is a general rule.

The performance increase should be very limited (less than 15% or so, haven’t measured it though). Main advantages of a dedicated CUDA GPU are the lifting of the 2…5s watchdog timer runtime limit, and the ability to debug GPU code on the device.