In one year ago I just upgraded to 8mbps. speedtest.net shows 8mbps, but downloading never exceeds 450KBS. I changed router too. I read online that most of old router have a problem maintaining throughput, so I bought a new tplink router.
Airtel guys are very clever, if you tracert speedtest.net, you will notice, the data passes through specific router 59.14..*. Now tracert outher website, you will know the difference.
8mbps is total FARCE!