Just a quick FYI... even if your "super router" (HG633) reports a decent sync speed, a poor cable between the router and the master VDSL socket can still have a severe detrimental effect, in my experience at least.
I've been using an HG633, not becuase it's much cop (wireless v poor etc) but simply as a replacement for the OpenReach modem if only because it has a web interface where I can see the VDSL stats. I turn off wifi on the HG633 and put my normal router (ASUS RT-N66U) in the DMZ of the HG633 and that router then feeds my internal network (plus dual band home and guest wifi networks etc).
So while the HG633 reports a sync speed of about 60Mb (theoretical max 75) and a speedtest throughput of 55Mb, I moved some of my equipment around and replaced the RJ11 cable between the VDSL faceplate and the modem with a longer flat cable. On reconnecting, and allowing a few days for the speeds to settle, the HG633 was reporting a sync speed of 49 (theoretical max of 60). But actual throughput was a disaster - typically only 5 or 10 Mb at best, and at times as low as 1.5Mb.
With the wrong cable, sync speed drops only 20%, but actual throughput drops by 80% or more !
The modem might be able to sync at a decent speed, but when it comes to actually pumping data down the line, something is going very wrong.
I verified this effect over several days (to allow for DSLAM tuning) and times of day (to allow for network traffic), and it was pretty consistent (and yes, I ensured the ends were properly plugged in, and checked the cable for physical damage etc).
Replacing the cable with a similar length of non-flat RJ11 cable (a shielded twisted pair cable I had lying around, about £5-10) had an immediate effect. The modem immediately reports a sync speed of 58 (theoretical max 73) again, and actual throughput jumps back to 50. I expect a few days of stability may allow DSLAM training etc to edge that up slightly.
So don't believe that a decent sync speed automatically translates into decent throughput - try a decent shielded cable to the modem (keeping it as short as possible) and you may see real-world improvements.