I have the 350Mb service from VM, I use the SH3 in modem mode connected to my own router, all speedtest sites show 380+Mb/s down and 21Mb/s up except the TBB one, there's thread discussing that here in the Virgin Media section.
If you game or any of the BB users game then I suggest you read this thread https://community.virginmedia.com/t5/Gaming-Support/...
on VM's own forum, currently at 392 pages at time of posting.
I'm not trying to give out any advice or opinion just that you research first as recommended with anything to make sure its suitable for you and your needs.
Also as suggested i would make sure you have an overlap period as VM can vary greatly from area to area, my son had the service in my area before me so he was the guinea pig.
Previously I was with Sky 40/10 service and just moved to VM as they gave me a better bundle for TV/Phone and BB after my Sky discount expired.