when comparing GPGPU benchmark, the load in GPU is differ that for rendering my friend
some GPU kernel can be completed in fraction of a second so you won't notice any load
OR
some calculations might not using all shader processor inside GPU because of bad coding/hardware limitations
on the other hand, for some calculations it might use a lot of time
so it is better to perform "sustainable performance" in some amount of time, rather that just one function and go
bad coding is baddd, but what about: "It is sooo hard to code in AMD/ATI GPU"