I was thinking more on the side of, will the CPU be able to down-clock, lower than its stock clock, if the power isn't required - or is the stock clock the minimum it will always run. My desktop i7 920 had a base clock of 2.6ghz but would dynamically underlock to like 900-1000 mhz when the power wasn't required (Intel Speed step technology is it?).
A lot of the time, be it light browsing or just coding, I won't even need 1ghz of processing power (comparing to say an m3 rMB). But during these times, if it will still clock at 2.9ghz, I can see it being less of an optimal purchase as, it will only be really heavy compiling etc, which will happen infrequently, that would utilise the higher boost. And even then, I won't need pro-longed loads (just bursts) in which case the performance difference will be negligable, so is that processor altogether wasted?
Edit: http://ark.intel.com/products/91166/Intel-Core-i5-6267U-Processor-4M-Cache-up-to-3_30-GHz
Seems as though it does have Intel Speed Step technology, so it should be able to down-clock from base (unless Apple disables this by default?).