Me again....
I have tried this enhanced BruceX benchmark.
Regardless MacPro 7,1 or iMacPro 1,1 smbios, fist run result of 8k or 5k x3 is normal.
But as soon as I try the second or 3rd runs, the result will deteriorate quickly.
To get the reasonable result back, I had to quit FCPX and open it...