I486_CPU or I586_CPU in kernel config

[Warren Block]

Some time back, there was a post on one of the mailing lists that 
suggested it was better to leave either I486_CPU or I586_CPU enabled in 
a kernel config even for much newer processors.  For performance 
reasons, AFAIR.  Naturally I didn't save that post or a link to it.

Can anyone find that message, or explain why it would be good to keep 
either of those cpu options in a kernel that will only run on much newer 
CPUs?