Gel Resolution 9 Size Peoblem

Hello everyone, I cant decide which size of Gel Resolution 9 I should use. I try size 40.5 and 41.5 and both of them feels fine lengthwise. I mean there are half thumb space on front in both of them. Of course the smaller size feels tighter. But what is the best choice or how can I determine it? I currently own a 41.5, first 2 weeks it felt too big, but then either the break-in period or my feet got used to the shoe and it feels fine now. Now I bought a 40.5 to try but I not sure if I should return it or not. Any help?