Just upgraded to vivid 200 and superhub 3 after diminishing performance of original superhub. Unfortunately there has been no increase in download speeds, which are consistently 30-40mbs. Service status does not indicate any fault.
I've just gone from a SH2 to the Hub 3.0 and finding exactly the same thing on 2.4GHz (also have VIVID 200). This is frustrating as I could get ~167Mbps on 2.4GHz with the SH2. My theory is that the defaults of the Hub 3.0 are setup for wireless compatibility as opposed to performance. Usually there is an option to set the maximum connection rate for 2.4GHz 802.11n to various rates (SH2 had up to 300Mbps), but looking at the network stats on my PC it is now only connecting at 130Mbps which explains a max download of around 40Mbps.
Unfortunately there's nothing in the Hub 3.0 interface to change this. On the plus side if you have a 802.11ac compatible device then you should be able to get the maximum download from your package.
VirginMedia: Any news on an update that will expose any additional settings for getting the best from the Hub 3.0?
By default it uses 20MHz channels on 2.4GHz and 40MHz on 5GHz. This is actually good practice as it stops networks from eating too much local spectrum in crowded areas.
If you want the fastest speeds. Log into your SH3 and click Advanced settings > Wireless > Wireless signal and set the channel width for 2.4GHz to 20/40MHz. If you also have 802.11ac wireless devices, then also set the 5GHz channel width to 20/40/80MHz.
That should hopefully get your speeds back to what you expect!
Can't speak for the OP, but I thankfully don't have too much 2.4GHz congestion. Already had the 20/40MHz (and 20/40/80MHz for 5GHz) set and doesn't make any difference on any devices on 2.4GHz. Found the Arris user manual for the router hardware that the Hub 3 is based on so going to take a look though that, but could this be a bug in the Hub 3.0 not setting the channel width for 2.4 band correctly? 5GHz band is getting expected speeds.