Hi,
It is worth dropping an year for GATE to get an admit in IISc or one of the IITs. My suggestions will be that if you are dropping, join a good GATE institute. It will help you. Most of the time when we are preparing alone, we loose a sense of how good our preparation is as there is nothing to comapre it with. Joining an institute will help you maintain a reality check and those frequent test series there will help you to correctly assess your preparation.
When we drop (speaking from personal experience), we feel like we have almost an year and we can take things slow. But time will fly away in whipe. So do not waste time. Start early and finish early so that later you can devote more time to solve questions, which I feel is the key to crack GATE. Also when we join some coaching institute we feel like making friends and hang out with them after classes go to movies etc etc, please do not do that. There will be plenty of time to do that in the IISc or IITs. Be a loner, focus on the studies and remove all the distractions from your life. It will help a lot.
Hope this helps. All the best.