CPU usage alone doesn't mean much. A program could hardly take any CPU usage, and still be "slow". You also need to look at how many memory it uses (and in which segments), how many cache hits does it get, and how many page faults, how much I/O, how many (and which) system calls does it make, how many other resources does it use, etc, etc.

And also note that some measurements are very system dependent; they'll depend on the OS, the kernel configuration, the hardware installed, and what other processes are running on the box.

Abigail