If the ESRAM is 102GB/s as rumored I am going to throw this down as a prediction: 8 ROPs @ 800MHz. This is 6.4Gpixel/s and would require, yes, 102GB/s w/o MSAA if I did my math right.
And for giggles I will also predict Orbis (PS4) has 12 ROPs at 800MHz (9.6Gpixel/s requiring 152GB/s of bandwidth for peak fillrate with uncompressed data which modern GPUs make good use of).
If my above guesses are right based on the leaked data (???) Orbis doesn't only have a 50% higher compute (18CUs vs. 12CUs) but a large edge in Fillrate as well (50% more). If the TMUs hold firm at the same ratio, then Orbis is appearing to have 50% more GPU power across the board (Compute, Texturing, Fillrate).
I'm not sure how you can conclude the GPU performance is probably a wash, or that Durango ">" Orbis with respect to memory, or that either Durango or Orbis will lower their OS memory footprint over the life of the console.
There really isn't enough information out there to conclude any of those things. We've only seen a couple block diagrams and some vague information about the "data move engines" on Durango.
It is too early without (a) having confirmed specs of the final units and (b) some architectural insights.
That said things are looking very slanted toward Orbis.
Durango and Orbis
Compute: 12CUs and 18CUs -- 50% more compute
Fillrate: (guess) 8 ROPs and 12 ROPs -- 50% more fillrate
Cores (after OS): 6 Cores and 7 cores
Bandwidth (system)*: 68GB/s and 192GB/s
System Memory: 8GB and 4GB (5GB and 3.5GB after OS, respectively)
* 32MB ESRAM makes it an unlevel comparison.
We don't know the ESRAM bandwidth yet (or how it functions) but at 102GB/s we are looking at Orbis having more bandwidth -- and more flexible memory (2/3 of the Durango bandwidth would be tied up in a 32MB memory space).
This isn't like the 360 and PS3 where the architectures were very, very different. Both are using the same Jag cores and both are using AMD's GCN if the leaks are right. If that is the case the above numbers, if confirmed, and we know how the consoles function we can get a pretty good picture of what will be better more often than not.
Yep, all these notions that Sony's system won't be as efficient seems like a reach to me.
If AMD/NV know how to balance a GPU (I bet they do) then Pitcairn should be a pretty efficient GPU and investment of silicon. Obviously some units will always be idle in the pipeline but the key is striking a balance of ROPs, TMUs, and CUs to reach good efficiency. Seeing as Orbis is rumored to have a substantial amount of bandwidth (unlike RSX) it seems the system is tilted to make sure it runs as well as possible. Sure, would have a 64MB eDRAM module on top have helped alleviate one more issue? Sure. But designs are compromises and Sony seems to have made a safe, if uninspiring, bet. So far it looks to have been a really good one, too.