GetOutOfBox

Hi, I've had Zonealarm Internet Security for about a year now, and I've always noticed how it slows down my internet connection. I know this is to be expected, it examins packets as they enter the computer which is bound to slow down things, I'm not asking how to fix this, I just was thinking though, my ISP assigns dynamic IP's and my computer is not assigned a public IP. The router uses NAT routing to get stuff to me, so people can't remotely connect to my ip (192.168.*.*) unless their mad hackers and are determined to ruin me. I don't host any form of server other than the occasional gaming server, so I dont have more than 2 or 3 ports open, yes I know crackers can still get in through those ports, but the game servers I have don't have root access, so it would be quite a bit of work to get some shell code through my gameing server and install a rootkit, I don't have anything people would want on my computer. So what I'm asking is, will disabling my firewall greatly decrease my security, I know its going to a little bit, but I want more performance. Thanks in advance!