The claim is that there will be an improvement of 150 to 200% with integrated graphics. No way to tell as yet what the impact will be w/ discrete graphics. Undoubtedly there will be a increase in efficiency and therefore a lower TDP. Whether this results in extra overclock ability, we'll just have ti wait to find out.
As far as actual measurable speed improvements..... I have not seen anything so far to get me excited...... though Id say the same about Z68.....kinda like having a SATA III Hard Drive, yeah the bandwidth is bigger but the mechanical HD can't take advantage of it cause it doesn't even approach SATA II speeds. However, transfers from the HD cache do go at SATA III speeds so there is at least a marginal improvement.