Have been using Sify broadband for the past two years and the experience has been quite bad. All through I had a 256kbps connection and I have never seen the speeds go beyond 35Kbps (you can use the bandwidth meter available in https://cnet.com)! I have complained quite a few times and there has been no satisfactory response. My BIL uses Airtel 128Kbps unlimited download package and only when I recently used it I could see the difference - Airtel is amazingly fast! I am planning to switch to Airtel soon - I have contacted their marketing office but they are yet to respond (hope it is not a case of from the frying pan into the fire!)
Sify connection reliability is quite bad as well - the connection is through a broadband dialer which works only on WIndows. Many times when it shows that it has been connected I am actually not able to connect. Every time you double click the software and pray that it connects properly. The most recent version of the dialer refuses to work on Linux and eventheir customer support has no answers (the older version used to workbut now it is no longer compatible with the new version of the dialersoftware).
Also, there is no way of checking live how much you can download - you have to disconnect the session and reconnect to get this figure - this becomes a problem especially if you have a huge download planned.
The only better point is their customer service which atleast responds if there is a problem (though not always with a solution as stated above)!
All in all a product worth avoiding.