Hm, 1:29 and 1:41? You can't be serious? That's waaaaaay too slow for those GPUs.
Anyway,
The 150 sample is showing weird result for me also on CUDA. I've done my renders, which takes hours, on both CPU and GPU. From the results, I've understood that my CPU and 1060 are pretty much neck on neck.
However, in this 150 sample render, CUDA cores 17 seconds whereas my CPU cores 31 seconds. In 100 / 200 sample render, 1060 was identical to my CPU render time, 20 seconds / 40 seconds.
There may be a reason why AMD chose this specific 150 sample.