Apple A9X SoC

What do you mean by "entry-level"? The full iPad Pro has 51.2GB/s bandwidth. That's dual channel LPDDR4-3200, or in the range of top of the line Skylake DDR4 memory modules. Unless like Turbotab says, you are referring to the fact that its the launch speed?

 

My guess is they simply took out 2 of the 4 LPDDR4 chips in the big pro, while keeping everything else the same. The end result would be ~25GB/s for the small pro. It would explain why the CPU performance decrease is almost negligible while the GPU performance takes a large hit.

This way they can order the exact same LPDDR4 modules for both tablets and profit a bit more on a higher volume deal.

 

By entry-level I meant that LPDDR4 3200 (1600 MHz) seems to the standard spec available to those wanting to use LPDDR4 in their SoCs, there does not seem to be a lower clocked variant on offer, unless Apple is underclocking the RAM itself. I'm just trying to work out why Apple have seemingly reduced memory bandwidth much more than their advertised CPU/GPU comparisons, which indicate a reduction of around 5% CPU to 15% GPU.

With a smaller screen and far fewer pixels to push, combined with a downclocked CPU and GPU, you'd think the Pro 9.7 already had reduced its power consumption enough without cutting the memory bandwidth. The Pro 12.9 showed good sustained performance, and being fanless its SoC must be well under the 10W range.
http://www.apple.com/ipad/compare/

 

Ifixit have torn down the iPad Pro 9.7, and report a single 2GB RAM module, does this limit them to single channel in terms of RAM?, if so it would explain the much lower memory / GPU scores than on the 12.9.
https://www.ifixit.com/Teardown/iPad+Pro+9.7-Inch+Teardown/60939

Orange = Samsung K3RG1G1 - 2 GB (16 Gb) LPDDR4 RAM