Hope this clarifies it some for you.
This is Widipedia on the 1600:
X1600 uses the RV530 core, a core that is quite a bit different from the RV515 or X1300 and the R520 of X1800. The X1600 is positioned to replace Radeon X600 and Radeon X700 as ATI's mid-range GPU.
It shares design philosophy with the X1900, in that it has a far different ratio of pixel shader processors. ATI has stated that the X1600 is designed with a far greater shader computational load, a prediction of future game workloads. Whereas the X1300 and X1800 have an equal pixel shader to texturing unit ratio, which targets a more equal workload of shaders and texturing in games, the RV530 of X1600 alters this to 12 pixel shaders and 4 texturing units. The chip's single "quad" has 3 pixel shader processors per pipeline. This means the chip has the same texturing ability as the X1300 at the same clock speed, but with its 12 pixel shaders it encroaches on X1800's territory in shader computational performance. While the performance is no where near that of an x1800 it still manages to lead the x1300 by a decent margin across the board. The X1600 also receives a boost in the vertex shader department, with the addition of 3 more units (total of 5) over the X1300.
The X1600's core clock speeds are similar to X1300's while the memory attached is usually clocked higher. However, benchmarks shows that the X1600 is a decent step up from the x1300. The reasons for this is that the X1600 while having some of the same limitations has much greater ability to process complex shaders having triple the number of pipelines.