I have made a few discoveries using a free speed test app on our IPADs. This is after signing up for an ultra fast cable connection from Virgin Media in the UK. On a good day my download speed on an IPAD 4 (bought last September) is over 80 Mpbs but my wife's IPAD Air will record in excess of 110 Mpbs under identical conditions. Both have had all background apps closed before beginning the tests. My IPAD 4 has more apps installed. The test used was OOKLA.
Upload speeds are around 11.5 - 12.0 Mpbs using the cable service, but are a bit higher using 4G cellular connection, which produces very slow download speeds of around 6 Mpbs.
If the cable speeds drop off this can be due either to server problems miles down the cable, or router problems. A quick fix is to unplug your router for a minute, or reset this. Speeds will definitely be lower during times of high internet usage across the cable network.
As for streaming this is usually very good, but the Amazon service produces blurred areas on our TV screen. Not easy to compare with Netflix, as this is mostly watched through a cable app on the TV service.
Remember that stuff used to buffer a lot using telephone line internet and a 2006 laptop - we used to blame the programme providers - Netflix, BBC, etc at the time.