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Firstly Virgin Media don't support - as in provide assistance - routers. Thus they won't recommend to avoid getting into dodgy ground when a customer has issues.
Torrents generally can expose weaknesses in kit that other useage gets away with. It's nothing to do with traffic shaping which is applied at Virgin Media's end, wheras the problems you are seeing are clearly in your router, or use of it.
There are some basics - firstly your upload speed of any torrents should be no more than 80% of the total speed available (if you get shaped remember your upload speed drops so your torrent speed also needs to be adjusted). Similarly limit your download bandwidth, especially if you have someone else using the internet while the torrents are running.
Now look at how many connections are being maintained by your torrent client. Torrents work by throwing out lots of messages trying to find others who have / or want the stuff you are sharing. These connections can get refreshed very frequently. This can overwhelm the router's memory. Certainly the earlier versions of the Linksys WRT54G series suffered from this. Third party firmware (DD_WRT for example) can help reduce this problem, but you still have to adjust some retention settings in the router.
Finally, and perhaps the biggest problem, by moving to the top tier internet speed, chances are you are now mixing it with all the other big boy users in your area. Contention issues could be having an effect.