My experience suggests that 270px high will work. from what i can tell, and I’m no css expert, there is a 372 max height on the slider and a 3em buffer from the top. My measurements suggest that 270px will leave a similar height buffer on the bottom of the image you have used.
I am dealing with a different issue related to the sliders: they only work up to a max width of 1280px. if you grow your browser window wider than 1280px the image and text become centered in the slider area.