Apache2の新Ver.に入れ換える際、MPMをpreforkからworkerに変更してみました。
何だかそれなりに良さげな感じです。

Server Software: Apache/2.0.49
Server Hostname: localhost
Server Port: 80
Document Path: /index.html.en
Document Length: 1456 bytes
Concurrency Level: 10
Time taken for tests: 2.892277 seconds
Complete requests: 10000
Failed requests: 0
Write errors: 0
Total transferred: 16980000 bytes
HTML transferred: 14560000 bytes
Requests per second: 3457.48 [#/sec] (mean)
Time per request: 2.892 [ms] (mean)
Time per request: 0.289 [ms] (mean, across all concurrent requests)
Transfer rate: 5733.20 [Kbytes/sec] received
Connection Times (ms)
min mean[+/-sd] median max
Connect: 0 0 0.0 0 2
Processing: 0 2 0.6 2 9
Waiting: 0 0 1.2 1 8
Total: 0 2 0.6 2 9
Percentage of the requests served within a certain time (ms)
50% 2
66% 2
75% 2
80% 2
90% 2
95% 3
98% 4
99% 5
100% 9 (longest request)