your confused.... it's 3.8m/BIT not 3.8 m/BYTE!

if you have a 4mb line it doesnt mean you can download at 4 megabytes per second

300kb/s is about right for the line speed you are on

which is what that test shows.

speedtest shows your line speed in k/bit which is 4000k/bit - that test you showed was in k/bytes. the download speed your computer will show on a bitorrent/internet explorer download. 8 bits in a byte