As long as there is room to tighten the buckle I would go with the 43. Your feet will swell a bit on long rides and as everyone said having shoes that are too tight will not work. The only issue I see is that shoes may stretch a bit and if you don't have the ability to tighten them they may turn out too loose in the future. I know with the shoes I have I had about 2 clicks left when I got them and now I am all of the way down to the stop, so next time I plan to go one size smaller.