Download speed much much lower than test result??

[#1]

Hello there, as a new costumer to Plusnet my line speed was measured at >5Mbps at sign up and installation, and whenever the BT whole speed test is conducted the speed is listed as this (5Mbps) (both wireless and wired test). However whenever a download is happening be it via Steam, a document, a thesis paper, a mod for a game, a movie or anything the speed seems to be capped at around 600Kbps via line or wireless, and hence is much much slower than I was told the speed would be. I waited the 10 days to see if any difference was found, and although the connection is more stable the speed is still very poor and capped at this 600Kbps...
After calling Plusnet help I was recommended to change my wireless channel and this was done however not much difference at all was found and I have reset the setting to standard.
Please if any help could be given that would be great as the speed is much much lower than I expected and is making downloads quite a hassle.  

Gumball

[#2]

Are you mixing up the units of bits and bytes perhaps?
5000kbit/s = 625kByte/s
Broadband is advertised with speeds based on bits, and speedtesters give results in bits (or multiples thereof, kb/s or Mb/s). There are 8 bits in a byte, and most programs will report download speeds in bytes (or multiples, kB/s or MB/s).

[#3]

Ah this may be the case! My speeds today were clocking in around 0.16MB so I will see if they improve!

[#4]

As ejs has advised it's probably the difference between Mb/s and MB/s.
I'm not sure if there's a way you can change the way Steam shows the download speed but it may be worth looking for.