Are the number of Stream Processors the most effective specification to directly relate a specific GPU to hash/s metrics?

For instance:

My ATI "Redwood" has 400 stream processors and can push about 36,000 khash/s.  (@90 khash/s per stream)

An ATI HD 5970 can put out 560,000 khash/s with 3,200 stream processors (@175 khash/s per stream)

My NVidia Quadra NVS 135M has 8 stream processors (hahah!) and does 950 khash/s  (@~120 khash/s per stream)


Other metrics don't seem to matter that much, i.e. GPU memory and memory speed, GPU clock speed, bus width, etc.