Never done a solo ton but think I could probably just about stomach one. I like fastish solo rides of about 70 miles in length - tend to start getting a bit bored by then or need to get back to rest the legs (don't stop much when riding on my todd).
Regards to avg speeds, I sometimes think the increase because of riding with others is overplayed a little. I seem to do the same speed if not faster when I am by myself but it's probably down to having the road to yourself and being able to push it a little bit harder anytime you please. Drafting does give a speed boost, for sure but I myself have only found it to be of any real benefit when you are cruising at brisker speeds. Same effort level for 19mph solo, as yields 21-22 in a group, in my experience anyway.
This post is a rambling mess and not much to do with Strava racing - sorry... as you were