what size should i buy ?
SIDI size chart says 290 mm is Euro 43.5
I'm 270mm and wear 43 SiDi in both road and mtb. Don't forget that they're narrow so length might not be the limiting factor. 290 hints at 45/46.
What's stopping you from trying a pair on? That's got to be better than internet muppets sticking their fingers in the air.