If it test fine in speedtest then your connection is fine. You will notice that if you choose other speedtest locations it can be slower. The sites you are downloading from maybe farther from your house and they may be have other limitation. I know steam will download some games at my maximum rate and other it download slow for no reason I could ever find.
Another thing to point out is speedtest has rates in bits/sec where file downloads are generally in bytes/sec so will be 1/8 the number