 At max 10 wavefronts can be attributed per SIMD-VU (thus 40 per CU).AMD CodeXL shows tables with the relationship between number of SGPRs and VGPRs to the number of wavefronts, but basically for SGPRS it is min(104, 512/numwavefronts) and VGPRS 256/numwavefronts.Note that in conjunction with the SSE instructions this concept of most basic level of parallelism is often called a "vector width".