you can't adjust buffers on a CSS.
The CSS does not accept ICMP fragment, so you can't ping the vip with packet size bigger than MTU.
Finally, if you want to test CSS performance, you need to use UDP or TCP traffic - not icmp.
I don't know what are the CP and TI devices, but if you suspect a problem, the first option is to capture a sniffer trace of the traffic on both the CP device and the TI device simultaneously so we can see where a delay exist and who is the culprit.
Do the same test without the CSS if possible.
Regards,
Gilles.