I finally managed to get an ADSL2+ connection to my house! This has however caused lots of frustration in getting it to work! From my research, it looks like the Netgear DG834 modem does not like a lot of ADSL2+ lines.
I have one of these modems at a friends place and it seems to sync up using ADSL2+ and gets a nice 10Mbit connection. Mine however will not sync at all in ADSL2+ mode... It's interesting that using ADSL1 (G.DMT), the modem will sync at ~5Mbit downstream - which is what I was expecting seeing as my Cisco router would report a max attainable line speed of around 5Mbit.
If I lock the Netgear DG834 to ADSL2+ mode, it will not sync at all. I talked to Netgear about this and they did the good old "it's the ISPs fault" and didn't really want to hear anything more. In the meantime, I'm getting my ISP (Spin Internet - I'd recommend them to anyone!) to send me a Billion 7300 modem which they say seems to have no issues.
Will be interesting to see if the Netgear DG834 modem is just no good at ADSL2+!