CP achilles low sizing

Hey guys, i need some advice for the sizing on the achilles low. I wear 9UK (43 1/3 EU) in ultra boost and the wings and horns R2s (i have quiet some room, but if i get a UK 8.5 my big toe always peaks out strangely). Should i get a 41 42 or 43 for the Cps? Thanks for your help