According to GPUShaderAnalyzer you get more ALU power disabling address virtualization (however it reports most kernels are TEX limited in this mode, so little performance advantage is expected).
The current version of Brook+ has a flag to disable this feature, can you explain a bit more about this?
What's the maximum stream size without it?
Can you still use 1D and 3D streams?
Does it work properly? Are there any drawbacks?
Thanks