If you had one site putting pulling as much bandwidth as it could and 83 sites doing nothing - that site would get 500Mb/s. However your spokes have an MX64 class device, which can do 100Mb/s, so it would actually be limited by the spoke to 100Mb/s.
If you had two sites putting pulling as much bandwidth as they could and 82 sites doing nothing - those two sites would get 250Mb/s each. However your spokes have an MX64 class device, which can do 100Mb/s, so it would actually be limited by the spoke to 100Mb/s.
If you had three sites putting pulling as much bandwidth as they could and 81 sites doing nothing - those three sites would get 166Mb/s each. However your spokes have an MX64 class device, which can do 100Mb/s, so it would actually be limited by the spoke to 100Mb/s.
If you had 84 sites using RDS each only able to pull 1Mb/s each because that is all that RDS is needing, then each site would get 1Mb/s (well under the total of 500Mb/s).
If all 84 sites were able to pull as much bandwidth as they could then they would get 500/84 - just under 6Mb/s each.
Unless you are doing something that saturates bandwidth constantly, like video surveillance, you can typically oversubscribe the sites as they won't be able to pull as much bandwidth as they can - they'll only pull enough bandwidth to complete the jobs they are trying to do. You would have to measure that number yourself for your own network.
Let's pretend you are using a 20:1 oversubscription ratio. Each site would get an average of just under 30Mb/s.