There are some charts from the Measuring Broadband America reports that show what thousands of users cumulative experiences have been.
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www.fcc.gov/measuring-br ··· #Chart10»
www.fcc.gov/measuring-br ··· #Chart12As you can see, your experience is not far off from what many others have seen. Above 15 Mbps, there is only about a 10% decrease in load times for a 75 Mbps connection.
The advantage is what you noted, the ability to do multiple simultaneous downloads or uploads with little degradation of any one download's data transfer rate.
So, with a 1 Gigabit symmetrical fiber connection you can probably do 4 different Full HDTV(1080p) Netflix downloads/streams simultaneously. At the same time you can be uploading 4 different Full HDTV(1080p) home videos to some cloud storage. In addition you can have 4 simultaneous video chats going on, while all 4 users wander through the World Wide Web. You can add in a multiple camera home security system recording to the cloud, and you still should not see any problems for any of those uses. Basically 32 HDTV feeds simultaneously with 15.625 Mbps easily available for each data transfer. A total of 500 Mbps. The other 500 Mbps can be available for routine cloud backups, software updates, security, and other applications running in the background.
That is an example of the advantages of a really capable fiber optic internet connection.