Lets do some math:
5 GB = 5,000,000 KB = 40,000,000 Kb
40,000,000 Kb / 30 days = 1,333,333 Kb / day
1,333,333 Kb / 24 hours = 55,556 Kb / hour
55,556 Kb / 60 minutes = 926 Kb / minute
926 Kb / 60 seconds = 15 Kb / second
This means that you could constantly download at 15 Kb/s for an entire month to fill that entire "cap". There is no way that anyone would would be able to, or want to do such a thing though, so a more practical number would be necessary in order to understand data usage.
Starting back at our
1,333,333 Kb / day number, lets see how much time each day we can have at full speed (we'll assume 1,200 Kb/s):
1,333,333 Kb / 1,200 Kb/s = 1,111 seconds
1,111 seconds is around 18 and a half minutes of full speed downloads a day. Forget about torrenting.
Enjoy