6870 = 1120 shaders / 56 texture units / 32 RoPs / 134 GB/s memory bw.
7770 = 896 shaders / 56 texture units / 16 RoPs / 88 GB/s memory bw.
Assumeing VLIW wastes like ~20% shaders because of VLIW4,....
the 7770 could be pretty close in performance.
That doesn't make any sense. HD7970 is 925 x 2048 vs. HD6970 with 880 x 1536 = 40%
The performance increase is commensurate with shading peformance increase. You can't just magically penalize HD6870's 1120 shaders by 20% vs. HD7770. The level of utilization of VLIW-4 architecture depends on the coding of the application. Your comparison also completely ignores that a videocard's performance is affected by 5 key parameters (GPU clocks, SPs, ROPs, TMUs and memory bandwidth). GPU clocks are the same, so we can leave that one out.
HD7970 also brought 50% more memory bandwidth, 40% more TMU performance and >50% ROP performance (because 32 ROPs in Tahiti XT are 50% faster than Cayman's and clock speed went up 5%). Strangely, you are completely discounting HD6870's ROP and memory bandwidth advantage over HD7770 and focusing entirely on the SPs. You are also ignoring that HD7770 has no tangible texture performance advantage.
If we assume the 7770 overclocks like the 7970 does,
this card will walk all over the 6870's once you overclock them.
Unlikely. The card which has a strong shot at making HD6870 obsolete is the HD7790, but it has an MSRP of $199, while HD6870s currently sell for $140.
HD7770 is going to be lucky enough to beat an HD6850. Considering it will have an MSRP of $149 and come out more than a year later, that's pretty disappointing. Technically speaking based on launch MSRPs, the closest replacement for HD6870 is HD7850 ($239 vs. $249 MSRP). In that regard, the 7850 is going to be a better card. Of course HD6870 doesn't sell at $239 today though. It's reasonable to estimate that by the time HD7850 actually launches, it'll be competing with GTX570s/ HD6950 2GBs.
It actually looks like the move to 28-nm may not bring much of a performance improvement in the entire part of the Radeon lineup below $359. Even HD7870 looks barely as good as the HD6970 for $299, but of course you can get an HD6950 for $240 today and unlock it to 6970 speeds.
This is a repeat of HD5750/5770 and HD6850/6870 launches. The MSRP prices made all of those cards far less attractive than the cheaper and equally or faster performaning previous generation cards (HD4870/4890/GTX260 216 and HD5850/5870, etc.). Over time, all those MSRP prices actually fell to reasonable levels where those cards became worth buying. We've seen NV do the same thing with their ridiculous pricing for GTX550 Ti.
I would always wait for MSRP for low-end and mid-range cards to drop because lately AMD and NV have been way too amitious with MSRPs at this level of cards. It's one thing to charge higher premium for HD7970 since well it's the fastest single-GPU. But to bring out an entirely new line-up of 28nm cards at prices that make your previous line-up look as good seems underwhelming at the moment.
The recycling of 5770 is over with 7770, 28nm and a new architecture.
Finally. By the time HD7770 actually launches at $149, it will go head on against HD6870 and GTX560, not against HD5770/6770. So will this new card actually elevate the performance level at the real world ~ $150 price level?
Facebook
Twitter