I have run ICS, a Netgear router, and now a Freesco router. If you play online games, depending on which ones you play, you might find it easier to stay with ICS. That way you will have the outside IP going to your machine and will not have to forward any ports, that is if the games you play require it. If it is better performance in internet traffic, you will not see any improvement. I used to use a 200mhz P1 and it did ICS as well as my 800. No difference there. I actually found that ICS and my P3 800 would handle high bandwith better then the Netgear router. Gamespy for example, would update Half-Life servers in half the time.
"ICS is not only hard to setup"
This I do not understand as is as simple as adding the router in the network, besides that he already has ICS running.
If better performance is the only reason you want to change then I would not even bother. If you want better security and lots of features skip the Gateway/router and build a Freesco box. If I did not have my Freesco box I would just use ICS as it works better then my Netgear router.