Unless they've changed a lot from the originals, I found they don't stretch a huge amount. I've always found Sportiva's sizing to be very large though, so I have to go down in size a lot more than for other boots. From size 45/46ish street shoes, I was always 44.5 in FiveTen, 43.5 in Scarpas and 42.5 in Miura and MiuraVS (half size smaller in Katanas, which stretch a fair bit). Great shoes though - particularly the VS.