Originally Posted by Benetanegia
There's no direct proof of that, obviously, however there's hundreds of evidences found on other cards, that demostrate that memory bandwidth is not a heavy limiting factor.
First of all you have to understand that HD7970 did NOT require all the bandwidth that it has. It does need more than HD6970, especially for compute, but it does not strictly need as much as it has. AMD did not have any other option than going 384 bits, because GDDR5 speeds higher than 1400 Mhz are not very doable and are very very expensive anyway. So their only option was a wider bus.
192 bit GTX460 has 86 GB/s BW
256 bit 460 has 115 GB/s, that's 33% more BW but performance difference is not much bigger than 5%.
Another example, GTX 480 vs GTX 570, evidence #2
GTX 480 has 177 GB/s
GTX 570 has 152 GB/s - it is slightly faster, despite the 480 having 16% more memory bandwidth.
So is HD7970 kind of performance posible with HD6970 kind of bandwidth? Absolutely.
PS: The HD5670 example you posted, GDDR5 vs GDDR3, you are talking about half the bandwidth which is not going to be the case with GK104 at all (if it really is 256 bit anyway). We would be talking about a 50% reduction is buss width, but an increase of 40% in clocks, for a net bandwidth loss of 10% compared to the GTX580, a card itself is probably NOT limited by it's memory bandwidth anyway.
You have NO proof but i have my proof.
3dm11 score of my GTX580@850 and stock BW
GTX580@850 and HD6970 BW ( 1835 mem clocks )
nuff said ???
ps. i know that in order to bring GTX580 to HD7970 level in 3dm11, i have to push my 580 almost 1000 core clock but 850 core is enough for proving.