I tried the solution in [Wayback/Archive.is] Fritz!box 7590 interface extremely slow : fritzbox (remove the some 30-40 unused machines from the network overview), but it didn’t matter: since Fritz!OS 7.x, the Fritz!Box 7490 UI is just very very slow: each page takes 10+ seconds to load.
Hopefully I can get rid of these and move to pfSense based hardware eventually.
–jeroen