I managed to test lsphp5 with suExec enabled and disabled under a cPanel server in our lab.
Code:
~>ab -k -n 20000 -c 100 192.168.0.81/test.php
suExec enabled:
Requests per second: 2723.91 [#/sec] (mean)
suExec diabled:(run as nobody)
Requests per second: 2659.31 [#/sec] (mean)
so no difference in benchmark -- above test without opcode cache.
for other questions -- may need other staff's reply.