I concur with him. Apache with php can stand 300X1000 requests. I suspect the bottleneck is on mysql...
The reason I gave the suggestion to do the ab with all default setting was trying to address the fact that you will need a baseline for your tunning effort. Without this baseline, it will be hard to tell if ur tunning works or not.
Also, I don't trust the benchmark tool like ab...
I will suggest u testing the mysql alone first...