So I posted this on Reddit and thought I should share it here. Setting values of 75-100 on this in your batch file can decrease rejects and increase WU size, therefor increasing your hashing efficiency. Most people on reddit are getting positive results.
setx GPU_MAX_HEAP_SIZE 100
This article provides information about the preview feature for accessing additional physical memory on the GPU from OpenCL™ applications in the ATI Stream SDK v2.2.
The ATI Stream SDK v2.2 currently defaults to exposing 50% of the physical GPU memory to OpenCL™ applications. Certain developers may require accessing additional physical memory in order to optimize their applications when running on the GPU.
For developers who wish to experiment with increasing the amount of physical memory that is accessible to their OpenCL™ applications, the default 50% setting can be changed by setting the environment variable GPU_MAX_HEAP_SIZE to the percentage of total GPU memory that should be exposed.
For example, if you wanted to set the exposed GPU physical memory size to 75%, you need to the GPU_MAX_HEAP_SIZE environment variable to 75.
GPU_MAX_HEAP_SIZE must be set to an integer value between 0 and 100, inclusive.
It should be noted that changing the default setting for exposed GPU physical memory to the OpenCL™ application may result in unexpected behavior. This preview feature is provided solely to allow developers to experiment with accessing a larger portion of the GPU physical memory than is normally
