Router with Firewall adds 6Mb speed reduction!

I'm wondering if anyone has any links or information on the latency added by various routers built in firewalls?

I really didn't both checking much before, but last night my download speeds got the best of me and I decided to run some speed tests. I was getting regularly 3.5Mb download and a full 1Mb upload; my service is supposed to be 10Mb download - the upload speed is, however, correct.

After some gnashing of teeth, I disconnected the router (Linksys RVL200) and connected directly into one of my PC's and lo-and-behold I was getting 9.8Mb download (Btw - I used my ISP's speed test so that it would be local - and not impacted my general network latencies to diverse other speed testing sites).

I connected through my router, and it dropped back to 3.5, I checked all the settings, and finally decided to see if the firewall was causing latency, and as soon as I turned it off - I was back to 9.8! It is very consistent - a 6 - 6.5Mb latency introduction. It seems that the in-router firewall is not very efficient.

So, the question is, does anyone know of any comparisons done that show the latency introduced by different consumer based router/firewall combos?

Please don't just say use Linux - (a) that's not the question, (b) I'd use Solaris first, (c) I've been a sys-admin for the past 20 yrs and at this point in time, when I go home, I don't want to worry about configuring more systems that my wife and kids will be confused by. The consumer based router/firewall also takes up less space - I've already got 11 servers and PC's sitting around for various testing and work - and I moved from a server based firewall about a year or two ago.

Thanks
-ahg