I know this may sound really dumb but have you double checked that Virgin have actually upgraded your speed? Also, have you tried resetting your router?
If you are supposed to be on Virgin's 350 service but are only getting 50mb or so then there is definitely an issue. There can be a number of reasons why your speed is so bad. However, you definitely need to get on to Virgin support and get them to thoroughly investigate this issue with an Engineer on site too.
What device are you checking the speed on? Is it a desktop PC, a laptop or a gaming console etc? This is the first important question that you need to answer. Then the second is what type of Virgin Hub do you have? I think someone pointed out that it isn't a Hub 3 by the looks of the settings. This shouldnt matter too much but the Hub 3 is far superior to the Hub 2 etc.
If you are experiencing lag when playing then that could be caused by a number of factors too starting with your device and other devices connected to your broadband. If you are playing a game and two other people are streaming movies and downloading etc then that can effect it no matter what the download speed is.
Anyway, you need to tell us what device you are using to measure the speed on and what network card does it have, is it a 1gb enabled card? If you are using a desktop PC with a 1GB network card then try swapping your network cable for a new one. I have had a faulty cable in the past limiting my speed to 100mb. Worth a shot.