We can and sometimes do run Stack Overflow (currently 3.3 billions hit a month) from 2 web servers and 1 SQL server...I think that's pretty good for any stack.
(Not that that your performance sounds like a compelling advantage for that stack. That's what, an average of 700 requests/second/web server? So the peak is probably around 1500? Pretty good indeed, but not outstandingly so - where I worked 3 years ago our system handled peaks of 600 requests/second/web server on a JVM-based stack. And I don't see .net topping the charts on http://www.techempower.com/benchmarks/).
You have to keep in mind we're ridiculously over-provisioned, we're handling that load while maintaining 10-15% utilization on 3 year old web servers. Also, we're rendering quite a bit of dynamic data when rendering each page in < 40ms (the average for a question page on Stack Overflow yesterday was 36ms).
We render every request we get in a very speedy manner, usually with 90% headroom and utilizing only 1 DB server (also at only 10-15% utilization)...we're pretty happy with that.
So you've premature-optimized for performance far past the point where you gained anything from it?
I'm not saying you shouldn't be happy with your performance, but if the best thing you can say about your platform is "it has adequate performance" then, well, it's not a very compelling platform.
It's an awesome platform for us and we love it...you should choose whatever platform works for you.
If you select the 'Win' hardware tab near the top of the page, you'll be able to see figures for Windows as well: http://www.techempower.com/benchmarks/#section=data-r6&hw=wi...
I've several friends working in that stack. While many defend it as the correct decision at the time (and I don't disagree with that), all would rather be using something else now.