I’ve tried the Shimanos in store while owning the Giros. I wear 42 for the Giro, but would have had to size down to get the necessary fit on the shimano with my narrow feet. I didn’t get them because with the 41, I didn’t have enough space in the toebox.
So I think it depends whether you have narrow feet that fit the Giro (a traditionally narrow last) or if you have normal width feet that you had to size up for. If your Giro’s fit well then you may encounter the same problem I had, but I am very narrow…
If there’s a return feature I’d order a couple sizes and return the ones that don’t work!