I just added a folder with some pictures and videos (~80 MB) to my Dropbox folder. Dropbox started syncing, and the "speed for browsing" dropped to unusable (DNS resolving pretty slow, websites loaded very slow or not loaded at all).
So I ran tracert to a couple of hosts and while Dropbox was syncing the reply time was between 2500ms and 3500ms or the hosts were unreachable. When I paused the Dropbox sync, the reply time almost immediately dropped to the usual 50-100ms.
Auto-limiting the Dropbox upload "improved" the reply times of tracert to 1500ms, but browsing was still painful.
I didn't experience this behavior in the past (or I didn't correlate slow internet to Dropbox sync), however I recently replaced my old Fritzbox 7170 router with a new Fritzbox 3370 (which should have at least much faster WiFi).
Any suggestions, which settings I should check?
I use cable (Kabel BW, Germany) for internet with 10Mbps download rate.