Speeds are OK, considering they provide an unlimited download quota. The Rs.1000 package is very fast because it is limited to 1GB.
When you gain from one end, you lose from another. That's the nature. Can't help it. SLT can't help it either. If you have contacts with the international ISPs, ask them to lower the tariffs charged by SLT for the bandwidth. Then SLT will lower the charges, keeping the same profit margin.
P.S.
All these people who say that they can download at 10Mbps or 24Mbps can't download as much as we can. They have a very small download limit. 10GB-20GB for normal. 40GB and more if you pay a big premium. Sure, their browsing speeds are out of this world, but they can't download as much as we can. If you really got into the download spree, you can download more than 100GB worth data within a month with 512k connection.