Re: Lag
TL;DR:
It's all about single-core CPU speed. The Snapdragon 805 is about half way between the A6 and A7 when it comes to single-core, and in real usage that's the speed you feel. The Note 4 can be 20%+ faster in single-core than a Note 3, but that advantage is almost certainly taken away by the higher screen res when you're doing normal phone stuff or scrolling up and down webpages.
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Between the marketing and the fact that review sites insist on focusing on multi-core benchmark scores you'd almost believe that Qualcomm's SoCs are comparable to Apple's SoCs, but it's just not true for one very important reason:
In real usage single-core is king. It's really, really hard to parallelize real-time lag-sensitive tasks. So hard that it's generally not done. What ends up happening with multiple cores is that they're each handed a job, but in most situations one of those jobs will be "rate determining." In other words one of the tasks, given to a single core, will take longer to complete than any of the others.
When this happens your perceived performance is now entirely based on single-core speed, and this is where the SoCs on the market are at a huge disadvantage to Apple's chips. Even in the best case scenario (a fully parallelized task that can use all cores) the thermal limits render any possible advantages from more cores meaningless. Both the iP6 and Note 4 cap out around 2800 (Geekbench) when they hit thermal limits for devices in the phone size range. This is why the A8X is the first 3-core SoC from Apple; the thermal overhead is finally available due to SoC optimizations combined with the large case.
So in practice your situation ranges from far slower to dead heat. While parallelization will continue to improve at the software level there are some tasks will remain difficult to multi-thread. A great example is the brush engine for Sketchbook, which has been stuck on a single core for a long time and even on desktop platforms shows no signs of changing soon (it's the worst case; real time and lag sensitive).
Basically if I'm at Qualcomm I'm pulling my hair out trying to figure out how to match Apple's single-core since until that happens these quad core SoCs are going to be slow in practical application.
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For some contrast this invalidates the claim I've been seeing that the Note 4 is not any faster than the 3 in CPU-bound tasks. Whenever I read this the reviewer immediately points to some multi-core benchmarks and says "look how similar they are." That would be correct if the normal work load was a well-threaded rendering job, as both chips hit the same thermal limit and throttle since they're similar architectures on the same process node.
In a real world situation the thermal limit won't come into play and the "rate limiting" core will run more or less at full speed. If the Geekbench numbers are accurate than this means the Note 4 can potentially be 25% faster in these situations. This is why you see a 20%+ improvement in things like the browser benchmarks Anandtech uses even while benchmark suites like Antutu or multi-core Geekbench report nearly identical scores
So why doesn't that translate into improved UI performance? Most likely these gains are being eaten by the increased screen res which ends up taxing the CPU more. Much of the pre-rendering UI compositing will be done by the CPU and doing that work at higher resolutions does increase the work load. (We saw this on the Retina MBP line where UI performance is bound by single-core CPU speed, not the GPU or multi-core CPU).
Where you can probably see some gains is when you're out of the UI in a 3rd party application that needs a lot of CPU power. Sketchbook is a great example. In this situation does the extra resolution balance things out to no net gain vs the Note 3? Without being able to compare the two side by side I can't say.
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If I were in charge of Samsung's product development I would have stuck with 1920x1080 and gone with a full RGB stripe. Instead they moved to a higher resolution, but stayed pentile, which is confusing to me. This means you only get slightly higher fidelity than RGB 1080P, but you have to render at full 2560x1440. It's a waste of CPU/GPU cycles for minimal benefit over a full 1080P subpixel layout.
I probably also would have waited for the snapdragon 810. Neither of these choices do anything to pad the spec sheet, so instead they went.. the way they did. I just hope they don't seriously go pentile 4K next year, because as it is 1080P (RGB) at this size is already over the line into seriously diminishing returns.
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Last bit: I just want to say that even though I have plenty of negative things to say here I am loving this device purely as a tiny Cintiq (with a PDP-like display, which is crazy impressive at night). Unless Apple suddenly decides to produce a "phablet" with a Wacom digitizer I think the Note line has a place in my device lineup. I'm not sure if I need a brand new one or whether I want it to be my phone, but now that I've had it I can't give up the pocket Cintiq as a concept.