Amp Extreme - Quiet fan for a high end card, already overclocked like a demon, good temperatures, 3+2 years warranty (if you register in the first week)..
Asus Strix - already overclocked a bit(not as much as amp extreme), Better VFM, 3 years warranty, Difference between Amp extreme and asus strix is about 6 fps in crysis 3..
Zotac Normal -Reference clock speed, Best VFM if you overclock slightly, but you will never reach Amp extreme levels without proper cooling, again 5 years warranty
IMO, go for the Zotac normal, Rs 5.8k more for 8-9 fps gains is definitely not worth it..
Performance wise:
Zotac Normal < ASUS Strix < Zotac Amp extreme < Zotac Amp Omega (not available in india)
You can check the reviews yourself on youtube (LinusTechTips)
PS: I myself dont know but you should find out how good Aditya Infotech is regarding zotac RMA.. for a 27k card, warranty is of vital importance and you should really be careful when choosing a brand..
But I can confirm ASUS warranty, atleast in my city is very good