Those things aren't going to hit 100 MH/s are you kidding? Try 10 MH/s.
The integer performance of a 6770M (what I have in my laptop) far outstrips what the HD4000 is capable of and it only gets 75 MH/s.
Hmm... I think 40-50 M/hash might be more realistic, then.
But at any rate, the HD 4000 is the most power efficient mining chip out there, with the exception of FPGAs.
2 MH/J is power efficient? What? Even at the proposed 100 MH/s (4MH/J) is not all that impressive.