Handbrake uses x264 encoder. x264 HD Benchmark
directly measures the time to encode a 720p24 MPEG-2 clip to H.264. Since Ver 5, the 720p24 clip has been replaced by a 1080p24 clip. This is the quickest way to compare the encoding performance of various CPUs (overclocked or not).
You can see users' results at Tech ARP Forums
. AnandTech Bench also includes x264 HD Benchmark.