AnandTech has a good article about what to expect from the A6 processor.
http://www.anandtech.com/show/4971/apple-iphone-4s-review-att-verizon/7 (note: numbers in this article are for the iPhone's A5 processor - the A5 processor in the iPad has higher clockspeeds).
It's really about expected that the A6 processor will be produced at a 28nm/32nm line (because Samsung and others are dumping the 45 nm line). This would allow a thinner, smaller processor which generates less heat and uses less energy. If Apple goes for a quad-core processor, it is very well possible it might use less energy than the current A5 processor.
What do you mean by thinner? Height? Likely the same and negligible in this case for any actual affects on product dimensions.
If we look at the architecture, really anything is possible. Apple has never stuck on the same architecture for more than two generations, but it's too soon to get a good pattern. It will be either the Cortex A9 architecture or the Cortex A15 architecture.
CPU clock? No one really knows right now. If the A6 processor indeed turns out to be a quad-core processor, than it's likely it's clocked at 1 GHz for iPad 3 and 800 MHz for iPhone 6. If the A6 processor turns out to be, for example, a dual core cortex A15-processor, than it could stay clocked at 1 GHz (A15 architecture is faster than the A9 architecture at the same clock speed) or it could be higher.
There are really lots of possibilities for the A6 processor. Apple could, however, play it very aggressively. Most companies try to avoid to move to a new process (like from 45 nm to 32 nm) ánd architecture at the same time. Apple, however, has already done so in the past: with the iPhone 3GS they moved from a 90nm process to 65nm process and they went from the ARM11 architecture to the Cortex A8 architecture.
It is different for licensed architectures. ARM targeted 28/32 nm processes with the A15 design. It would actually be a greater risk for someone to try the design on 40nm, and I don't think you'll see any. On the other hand, there's no reason to believe exynos 5250, omap 5, novathor 9600 etc. will debut on anything other than 28nm/32nm processes. If apple came out with that now, it would be a risky time to market because of the youth of the design and the process, not the simple combination of them.
Even if the next iPad had 512mb of ram, you wouldn't really notice because of the A6 (quad-core?).
RAM doesn't handle graphics, the graphics card does.![]()
Graphics depend on RAM too. SoCs traditionally have shared architectures when it comes to memory. Hopefully it will have LPDDR3 like the tegra 3.