I switched them after having previously had 8 accels before my speed and speed endurance. I originally switched them because I found that when I fatigued my accels, the acceleration portion of my speed and SE was weak and affected the rest of my run. When I switched them I didnt notice the opposite effect. Now mind you this was with 8x20m accels vs 4x30m accels. So I probably wouldnt have much problem doing those first. I still do accels in my warm up. But I like switching up the focus, and devoting slightly more energy to whatever I do first.