web server benchmarking

I am currently in a situation where I need to show to our board that our web servers are working at capacity. Can anyone point me towards throughput figures for web servers measured for different hardware/software platforms. Obviously, I would need rather recent data, i.e. benchmarks from before 2002 are not really of much value.
We are running a pair of DELL PowerEdge1850, 2GB RAM, 2×2.8 GHz CPU, Debian Linux (sarge), Apache 2.0, MySQL 4 (separate servers), so anything in this direction would be really appreciated.