Ra_V_en :
They don't do that at corporate level, you have CISCO hardware for that, not sure why anybody would try do it for home usage... well except of science
You do have a point: rolling your own router is fairly rare in the corporate world, but it is not unheard of. The corporate world is usually most interested in stability and standardization rather than speed and cost. Corporate world does not use overclocked cpus and gaming gpus.
There are plenty of vendors who will sell a router based on standard pc/server hardware. Doing it yourself is definitely a hobby niche, but it can pay off.
I'll be the voice of dissent: most $50-$200 routers easily overheat and crash. Their software is buggy. While they can handle the bandwidth, they may not be able to handle things like bittorrent traffic gracefully. Since they are a closed box, you cannot know how they will work until you use them. The companies that make them have little or no incentive to patch security holes or fix bugs They work fine for most things and when they die, they are easily replaced, but the OP asked for what is fastest. He could spend a ton on Cisco or Juniper and get something with way too many features that is difficult to configure. For personal use, I think it makes more sense to DIY.
A good compromise between DIY and high-end corporate routers could be MikroTik / routerboard.com routers. They are based on solid hardware, have well-maintained software (relative to the competition), and have reasonable cost for their hardware.