Ask HN: Logging activity to benchmark servers with?

Is there any software or methods to use to capture requests including posting text, images, etc that could then be used to benchmark the server with? Simply using same messages or randomising activity appears to be more time-consuming and not an indication of how users would use the service.

I plan to determine the best technology based on 'average' and 'high-load' activities as well potential worst-case scenarios based on use-cases.