Upload speed of the modem is depends on the internet service provider you are with.

Thank you.  I understand my ISP provider dictates this speed, but can this SB8200 handle 100Mbps Upload speed if I get it?

And what the difference between “Wired Speed” and “Best Cable Internet Speed”?

Thanks

Best internet speed for SB8200 is 1GB. Wired speed is totally depending on internet service provider.

Could you let me know your internet service provider?

My ISP provider is Xfinity with a 500mbps download and 100mbps UPLOAD speed (according to what they are telling me), but I can only get 25mbps upload speed when I run my speed tests.  I am using EERO Pro6 mesh system (3 nodes).

SB8200's maximum compatible speed for the upload is 40 Mbps. 

100Mbps, which is considered the Nexgen plan.

The Nexgen plan is not compatible with SB8200. Compatible devices for the Nexgen plan are the G54 and S34.