This is what Mark himself said
"they expect the gpu to spend
most of its time
at or
close to 2.23ghz and perfomance."
Doesn't it sound like, at times it cant even sustain
close to their marketed perfomance? As someone mentioned, even a 3-5% drop in frequency, brings its performance below 10TF, where a 5% loss , it becomes a 9.75TF machine
Thats also a draw back for depending on lower CUs + highly theoretical clocks.
Any small pecentage moves, it hits your perfomance harder.
MS is on to something with their 'sustained performance' attacks.