It would be a too perfect world if battery life were the same with dedicated graphics and the faster CPU . It's the dedicated graphics that use power more than the somewhat faster CPU. The machine automatically switches to Intel integrated graphics when unplugged, though you can override this. Mostly I use the ATI with the machine plugged in (gaming). But when I had used the ATI unplugged for Photoshop work, max runtimes were about an hour shorter (so 4 hours rather than 5). If you use it for even more demanding tasks, esp. 3D, it would probably take a greater toll.
-------------------- Lisa Gade Editor in Chief, MobileTechReview