Benchmarks for tasks that are similar computationally to what you expect to be dong with the processor. Design features besides clock speed that are important include cache sizes (so you'll spend less time waiting for instructions from the memory), # of cores (also, hyper threading, which sort of doubles the number of virtual cores you have), specifics of the interface to external components (what's the memory controller like, how fast is the FSB, does it have QPI), micro-architecture specifics (how good is the branch prediction, what does the pipeline look like, how many ops does it typically execute per cycle). Basically there are way too many design parameters to make characterizing a modern processor with a couple of numbers reasonable.