Be careful not to confuse MB (Megabytes) and Mb (Megabits).
Internet speed is generally measured in Megabits, but some apps/devices show Megabytes and people often confuse the two and think they're not getting the right speed.
The 350Mbps service should give you 43.75MBps (it will actually be a little bit over, as Virgin give you slightly more than the headline speed).
Your friend on 100Mbps should only get 12.5MBps. To get 100MBps or more, he would need the 1Gb service. (100MB = 800Mb).