Be value is £13.50 a month. No point paying more if your line doesn't support a faster speed (and frankly no point in paying more even if your line does).
As the user wants high usage then it is likely they may also want high speeds. I must admit I didn't list all of Be's packages and you are right value may do what they want - I only pointed out the 12 month cost to show them what could be saved on that package by a longer term contract.
And why is there no point paying more if you can get higher speeds? If you can get 20Mb (or 12, or 16, or whatever) and do a lot of downloading then an extra £4 a month may be well worth it.