I also think that it is extremely important to seperate "what you can do with a redhat cd and a dream" from "what someone can do with PC hardware". Absolutely correct ;)
The bottom line is: You are only going to get so much performance when you forward packets through a box which is processing an interrupt per packet, doing a patricia tree lookup per packet, copying the packet in memory a couple times, and doing some sequential comparisons through a firewall ruleset on every packet. None of the above has anything to do with PC hardware, but rather the poor software that people currently making "PC routers" choose to run.
If someone were to take *half* the software innovations which have been made over the past 15 years (a decent fib, interrupt coalescing, compiled packet matching rulesets, etc) and applied them as if they knew something about networking and coding, they could very easily produce a box using off the shelf PC hardware which woops up on a 7206vxr for somewhere less than $2000. If there is one thing PC hardware is good at, it is getting faster fast enough to keep up with the amount of bad code people keep churning out. :) Of course, then they would probably need to know a little bit more about routing protocols than just "how to compile zebra", but assuming they did that too... They would be bought by Cisco. :) You may find it interesting that both Linux and FreeBSD now have interrupt coalescing, and www.hipac.org is building a compiled ruleset.
As far as broken-ness of linux rib/route lookup code: Yes, it is so very 1985, but there may be changes coming soon [Pilosoft may be sponsoring a rewrite].
Anything else is either a cute playtoy for your house, or an endless source of laughter for the people who know better as they watch you work away at it. The vast majority of this discussion falls into the latter category, but after a while even this gem of a subject turns from funny to just plain sad. :) ...Until they get bought by Cisco? ;)