Dropbox is incredibly slow for me. I recently installed the Win10 tech preview on my desktop machine and it took overnight for it to download 15gb of Onedrive data over a wired cable modem connection that is capable of downloading at 12.5 megabytes per second. I then installed Onedrive on a MacBook Air and it took so long over the wireless connection that after about 4 hours I gave up and copied all the data off my Win10 pc onto a thumb drive and then copied from the thumb drive to the Air. I have looked this up on the internet and it is not an uncommon occurrence. iDrive and DropBox are much much faster, but I prefer Onedrive for many reasons, so I keep using it.
I think you're confusing your computer speed to your modem with the Internet speed which is probably more like a few mega bits (about one tenth of megabytes). The whole concept of cloud technology is for file syncing to take place in the background. Folks should poke some files into your cloud and than go about doing other things forget it & leave your Surface connected when you're not doing anything. I don't see any reason to be worrying about cloud syncing speed.