I mean based on how apple usually does things, it would seem unlikely that they would only get a 1-2 hour bump. Generally speaking, if they're going to work on something, like battery life, they make significant margins, or don't work it at all (from what I've seen in the past). So since the MBA's show it, plus obviously haswell incorporation, it would seem like maybe 10 hours or more would be expected. But Just logistically speaking, it seems like sort of a stretch.
But the more I think about it, the more it seems almost impossible for them to keep the dGPU this time around. Because battery life is almost certainly their goal, and also the gap between the 650M and the next "reasonable" dGPU is too far, plus the case for the MBPr really can't take any more heat output. So all of these things just make it seem so obvious they'd go iGPU. Sorry, side comment I guess.
They can make it 10+ hours by doing a few "tricks"...
1) Optimize software so that the CPU and iGPU can spend a lot more time idling than they do now. Thing is, though, software optimizations also benefit the older line, and... I'm indeed getting 7-8 hours more consistently with my 2012 rMBP 15" on Mavericks DP4. So in the end, even if Haswell gets 10+ hours, the old line may get close to 10 either way. And then there's still the dGPU and hundreds of dollars of price difference (between a new Haswell model and an old refurb) to consider.
2) Condense board space so that they can put in a bigger battery. This is possible on the 13" rMBP since you can tell from the dissecting videos that the 13" has a huge space (that fits a 2.5" drive) underneath the trackpad. Plus the 13" is sure to get a more power efficient chip (28W vs 35W), so the gain would be obvious. But the 15" rMBP is already hella cramped as it is, due to the gigantic battery (95WHr). And the 15" isn't getting a more power efficient CPU (47W vs 45W), so it's a harder bet.
3) A bit of a stretch, but they may have custom-ordered Haswell chips that are more power-efficient from Intel for the 15" as well. It's clear that even if they overclock Iris Pro, it would still lose out to the old 650M in a lot of cases. In that case, they might well turn around and concentrate more on battery life instead. Maybe underclock the Iris Pro chip so that it performs slightly slower, but then that allows the whole thing to be more power efficient. Then they can reduce cooling, and if there's less cooling, there's more space on the board for them to expand the battery. As above, the 13" definitely has more room for a bigger battery. So that's a done deal for the 13". But the 15" may need to cut corners in order to bump its battery capacity beyond that massive 95WHr, and I can't think of any other way than to shave off the size of the fans. But as stated, this is a bit of a stretch.
So my conclusion: 10+ hours is definitely possible with the 13" model, but it may not be possible with the 15" model.
