I’m on the 350 package. Download and uploads speeds are fine on my PC, tested using various websites including Speedtest,net.
So why then, are large files (say, 1GB and above) only uploading to Dropbox and Google Drive (ive not tried any others) at speeds no higher than 500KB/s, and on average half that. At the same time i can run a web based speed test and this shows no issues.
This is using the DB/GD Windows 10 apps, as well as trying different web browsers. Transferring the files across my home network gives me speeds of 50-60MB/s so its not my PC.
Disabled all security and that makes no difference.
I just setup an account for testing purposes on DropBox and it saturated my upload speed (I'm on the same 350Mbps package as you).
I think we need to determine if there is an issue on your line, even if it seems to be ok for other upload methods.
Could you access your router using http://192.168.0.1/ or http://192.168.100.1 for modem mode . You shouldn't need log in, select the 'Check Router Status' option and paste your 'Downstream', 'Upstream', and 'Network Log' tabs.