What does it mean when a %CPU exceeds (# of cores) x 100%?
The % CPU is relative to 1 core, so 726% is using almost 8 cores. Core is loosely defined, so 1 Hyper-Threaded, "virtual" core looks like 2 cores to Activity Monitor.

What type of system do you have? If it is just 2 cores (which is seems to be) then nik's answer sounds correct.

A late model 8-core system can look like 16 cores to Activity Monitor: