If you were to upgrade beyond the 100Mbps package, you'd currently likely need to install the development branch of Openwrt (until the next full release comes out), which has some significant performance improvements.
I'm not aware of any issues with its ADSL, it worked fine for me, however there is reportedly an issue with vectoring support on VDSL, but a fix seems to be close (vectoring not available on my line anyway):-
Also if running a mesh wifi on it on 5ghz radio, you need to uninstall the 5ghz -CT firmware and replace with the non-CT version.