CPU usage more than 100% on iMac

Most modern macs are dual core. Meaning essentially two processors are on one chip. In Activity Monitor on OSX, each core can be used up to 100% so, at full capacity, Activity Monitor will report 200-800% depending on the horsepower of your Mac. (some mac pros may exceed 800% or 8 cores)

The % CPU is relative to 1 core, so 726% is using almost 8 cores. A core is loosely defined, so 1 Hyper-Threaded, “virtual” core looks like 2 cores to Activity Monitor.