I tested the changes. I didn't see any real performance difference in my testing. Response times remained within a small margin of error with the old settings and with the new on a 256MB ALIX firewall and a 1GB PIV 2.8GHz desktop firewall.
However, the new settings did reduce the amount of memory used by php. Not that big a deal on the big memory machines, but a significant improvement on lower end machines.
So I've tweaked the settings a bit more. Changes from the last version:
1. Don't disable fast_cgi on tiny boxes. I misunderstood the previous settings and having fast_cgi enabled really makes a big difference even on a tiny box.
2. More aggressive settings for max_children and max_requests for "larger" boxes.
system.inc.txt