If your service is not blindingly fast, it is nowhere near 40 MBPS. the slower estimates are probably more accurate.
I worked for years with 1 MB service and I never had any complaint. Like I could watch a video and download another video at the same time with no interruption. Now I have something over 50 MB and it is noticeably faster, but not anything I care about because it was plenty fast enough even at 1 MB.