Use a Garmin or a smart phone and join Strava. It compares you to others who ride the same exact places you ride. Some are 1/2 mile segments (sections), some are 20 mile sections.
Very hard to say exactly what the answers may be but joining Strava gives you an idea.
45 mile flat ride I average 18.0 solo. 19.5 with a partner.
10 mile segment at 21.5.
While comparing myself to the speeds of others on the site, it varies due to wind, rain etc.
Some guys have posted faster times but they may be riding in a group, some with a big tailwind on a windy day, some may be riding against a big headwind so there are many variables to consider.
But Strava gives you a good idea of what you are doing compare to yourself and to others.
This is the top leader board for a local flat 10 miles section taken from Strava. As you can see the top guys are averaging 26-30 mph. I'm guessing they are riding in a pack of riders. But also I can see I am number 1482 out of 10907 riders that have ridden this segment. My best was 21.3 mph average over the 10 miles.
Like I said, Strava gives you a good idea of your accumulated efforts as well as those of others but there are variables to consider.