Wait till you have to contact customer care for some or the other reason and they show you the way to hell. I was on the same 256k Night Unlimited plan before switching to Airtel.
As you said, the speeds were great i.e when its running. Come rainy season and if the cables did not get cut by itself, they keep disconnecting the routers when ever they see a tiny rain drop fall from the sky and its all for your own good to save your computers from high voltage leakage into the cables they use. They started this trend when when some people sued their asses after electricity leaked into their cables and fried their computers.
Then comes the question of customer care. Their marketing people are ready enough to pester you to renew the connection even before the current plan is out, but if you have to call them up for some reason, its a miracle if they even pick up the phone, leave alone give a useful reply.
When I moved form one colony to the adjacent, I had to call the customer care to get the connection to my new place. After a month of pestering, which included e-mails to several VP's, CEO and senior marketing and customer care guy's, I got a serious response from their side. The local customer care manager along with he local cable wala decided I have to pay 3k towards installation charges again. They told me its the cost of the cable which is a joke considering that this cable costs peanuts in the market. They barely have to use 10~15m of cable for my new place. I was also not returned the cable from my previous place saying that even though its for the cable that I pay most of the installation charge for, its not returned back to me.
While this was all happening, I was being pestered by the marketing guy's to get my plan renewed even though I had not yet got them to install the cable for my new place. One guy even had a questionable (rude) tone saying that he has his targets to meet when I told him why should I renew when I did not even get my cable installed yet.
I got thoroughly fed up with them, walked to my local Airtel office and told them I wanted a connection, They took 500 bucks for installation and the next day, they were at my place. Their junction box was on the opposite side, so they did underground cabling without even damaging the road, they brought the cable into my house and properly covered it along the walls with PVC. The next day I had Internet access and I am yet to see downtime in the three years I had it. When ever I need to change plans, I just call up customer care and by next day the new plan is applied.
Airtel too does not have the best of customer care, but its a tonne better than Sify. Even with the download limits, Airtel is still a far better deal than Sify. If I have to choose between Sify, Airtel and Hell and If I cannot get Airtel for some reason, I would rather go to hell than choose Sify.