7950 can't get 900+ KH/s no matter what, so let's get this out of the way. If you'd pay attention, the hashrate at coinpolice was faked, some random person added there 2000 KH/s which upped the average by a lot.
what should i do if i get that worse Hynix /Elpida? Just return it and buy another one?
If you got them that means that in the first place you couldn't tell which type of memory your card has, so it's pointless to return and gamble again. What you can do however, is contact this guy:
https://litecointalk.org/index.php?topic=12369.0Read his post and you'll understand.
If i overclock/volt and max it out completely how much less lifetime will the card have?
Dunno, never overvolted and never will so I haven't got a clue how quickly the card will burn out. But one thing is certain, you will kill your card a lot faster than it normally would and I honestly can't see a reason to overvolt.
You know much more than I could find on search engines
Ive read the post and it says that Hynix has two variants: AFR and MFR. AFR is best then elpida and MFR is worst.The cause of being bad are the bad timings.Upload bios and send him donation so he will fix it.
"The ballpark value for the normal hash rate for Tahiti based cards is around: (Shaders * GPU Clock in GHz) * 0.34 >> (2048 * 1) * 0.34 = 696kHash/s."
This formula is very interesting it allows me to predict hash rate.How accurate is it? Where do 0.34 come from? can you explain formula?