US/UK GPA Conversion (for NITs & IITs), is it fair?

As I have found that US conversion of GPAs for GMAT admissions is quite different from what it should be. According to them 6/10 GPA in an IIT or NIT, is a 2.3 out of 4 on US Scale. While according to WES conversion, it accounts to *4/4 on US …

As I have found that US conversion of GPAs for GMAT admissions is quite different from what it should be.
According to them 6/10 GPA in an IIT or NIT, is a 2.3 out of 4 on US Scale. While according to WES conversion, it accounts to 4/4 on US scale. Is it valid to show WES transcripts for your grades?
Also, I would like to know if there is some sort of different conversion which top schools accepts for converting grades of NITians and IITians?
rolleyes
I am from NIT, Jaipur. I have scored 730 in GMAT, no work experience, and GPA of 6/10 in my college(yeah, its a bit low, as i was busy in NGOs and few other hobbies from music contests, organising cultural events and a lot more). So, how should I get a fair conversion out of it? How would they know that scoring grades in NITs and IITs is a little bit tougher than what it is in other colleges.
Is there any official documents that they accept for the conversion?