I think 24mm is the ideal focal length for taking high resolution panoramas.  The 36 megapixel Sony A7r gives a 450 megapixel equirectangular (30,000 x 15,000) which matches the resolution of the naked eye. 

Now I have a really good 24mm prime to shoot them with.  This test was shot at f/2.8, 3 rows of 8-around; developed in Lightroom to correct the considerable chromatic aberration; stitched with PTGui using 'exposure fusion' tone mapping.