@vishu Always had bias set between 55mu-60mu as recommended by Auris. I spoke to Tung-sol they said life is between 1000- 2000 hours. Thats is a big variation!!!!!
Opinions will vary - and while it may not be related, for reference I run my KT150s at 45-50ma, designer says I can go up to 60ma with no issue yet I have tried them as low as 40ma and they still sound pretty good. Currently running KT120s at 50ma too, good enough, no need to burn out tubes prematurely if you don't need to.
You'll see manufacturers reporting different life values between 2000-3000hrs for KT150s, and half the for KT120s and yet that can change for the better if you are not running the bias up too much. Ask your amp mfg/builder again on bias too.