From a quick glance on your post, I too suspect there is something wrong - your performance shouldn't be that bad, but there is not enough information to point where.
But, fortunately it's relatively easy to test. You get whatever server you prefer, and install nginx and install a bunch of performance testing tools (like siege, ab etc.) and then you test different concurrency load scenarios.
No custom software, and widely regarded the fastest webserver out there.
Yeah there's your problem...
Tux may be a bit faster, but it can't serve dynamic content nearly as fast as it serves files, so that's pretty much useless.
And you've written a webserver and you can't.
Interesting...