I have Shimano XM7 shoes in size 44 and Northwave Arctic Celsius in 45. I think the Arctic is the version with a fleecy lining, which may take up a little bit of space in the boot compared with yours.
The XM7s are a perfect fit, but I think from what I’ve read that they are wider than other/previous Shimano shoes/boots which people with wide feet did find required them to size up.
I tried the Northwave Arctic Celsius in both 44 and 45, and the 44 was too narrow for my feet, and I had to go with the 45s. They are possibly a bit big, but what struck me more was that they feel a bit like wearing a solid inflexible Tupperware box on my feet. I guess this is because they are fabricated from fairly rigid plastic, possibly using injection moulding to create the sole and upper together. However, when I am clipped in and riding they feel fine and I don’t notice this, but their rigidity is such that I would certainly not want to have walk miles in them if I had a major mechanical; in the same way I would not want to walk in carbon soled race shoes for a long distance. I am only wearing them in winter with De Feet Woolie Boolie socks.
For further comparison I take 44 in Sidi for which the standard fit is a bit too narrow, and the Mega wide fit is OK if a little bit wider than I would like.