7900 req/sec is on my laptop, first try without optimization - and we will need a lot more.

I know Disqus can serve up to 1M/server and they try to patch the Linux kernel to reach 2M. (Not exactly apples to apples since I use SQL transactions, but in the ballpark.)

The .NET never went over 440 request/sec on the server, not even with help from Microsoft. That means either C++ or using 2000 servers instead of the current 400 servers for every major deployment (hospital).

You're seriously serving a billion requests a day? And you're writing new software which is expected to go from zero to a billion requests, full stop? And you're not expecting anything to change between beginning development and production? And, once the software is in production, it's not going to change at all?

I seriously doubt that all of those things are true - in which case you'd probably be better off using a different language. In my experience, it's much, much cheaper to run 2000 servers ($10m capital cost? something like that?) than double the number of software engineers you've got ($Xm a year, continuously?), and doubling the number of software engineers isn't a linear scaling.

It's per deployment 2000 servers with C# or 400 with C++. And yes, it is currently used by the largest cancer center in USA (MD Anderson), DoD, VA, Kaiser etc to serve MRI, CT, XRay and similar images for diagnostics (PACS).

Then how is it new development? Your post doesn't make any sense in that context.

Furthermore, how optimized was the C#.NET version? C# will even let you drop into C++ if you want..I have a feeling the C# version may not have been tuned effectively.

Yeah I'd guess perhaps it was part of the framework. The CLR's unfortunate use of UCS-2 (2-byte per char) can really hurt in a string processing system. You can easily go from C# to native and back, so who knows. Also, "help from Microsoft" can range widely.