Maximum throughput webserver for images

Maximum throughput webserver for images

We need a simple/lightweight web server for small PNG (typically 50KB). We
will have several million.
We have done some testing with GoogleDrive which has an unknown web
server, but it does have SPDY support, which seems to really improve
download of batches of images (about 25 files/sec) currently.
We now need to standup our own server.
Any recommendations. Throughput of simple PNG files is the only goal. We
prefer open source Server Specs: Windows 2008 Server, 24+ GB memory, over
1TB disk, 8 core
WEBDAV support is a must.
I see that Apache 2 has a SPDY module: http://en.wikipedia.org/wiki/SPDY
There are some reviews at:
http://www.webperformance.com/load-testing/blog/2011/11/what-is-the-fastest-webserver/
LiteSpeed claims they are faster than Apache:
http://www.litespeedtech.com/overview.html But we don't need PHP scripts,
just fast downloads of PNG (and also JS, CSS)
It seems that the http://open.litespeedtech.com/mediawiki/ does not work
on Windows.