The Z97 motherboards are ideal, as they will support the upcoming 5th generation Broadwell processors, alongside Devil's Canyon too; which you already most likely know and includes the 4790K. Intel implies that the Devil's Canyon are better at overclocking, "
enhanced performance and overclocking." (
source) The improved TIM will most likely keep the CPU cooler, and as a result of the CPU being cooler, theoretically that should be another additional factor indicating that the DC can overclock greater.
Personally I believe it'll be better at overclocking than what we currently have. However I can't guarantee anything, as Devil's Canyon is still in early stages. We can't say for certain if the improved TIM will be able achieve greater cooling or not, or whether it's just minor.
That is of course all from my knowledge. I'm sure others on this forum have more expertise in this area than me.
All the best.