La sportiva muira vs sizing and stretch.

Just bought a pair of muira VS for red point burns on small edge climbs.  Bought them 1/2 size below street shoe size and although they feel perfect now (snug but comfortable enough for one pitch at a time) I’m a bit concerned that if they streach they wouldn’t work as well for hard for me (12b or so).

Thoughts?  How far down do u size?  I definitely don’t climb as well if my feet are uncomfortable. Would be stoked with little to no stretch.

I have solutions in the same size as the new muiras and after a year or so I’m still happy with them. 

They’ll stretch and get sloppy. I am 42.5 street, and I wear 40 in Futura, Genius and Katana. I bought 40 in Miura VS, and after having the same concerns as you, went to 39.5. These were perfect, but even these got sloppy come resole time.  I cannot imagine Miura in 42, which would be 0.5 size down. 

I'm down 1.5 sizes to a 41.5 vs. my 43 street shoe size. After the break-in period they're high-performing but still pretty comfortable for longer pitches which is what I wanted. I wore Skwamas/Solutions in a 41.5 as well and they were tighter/not as comfortable for sustained climbs but perfect for bouldering. If you want a really performance fit in the Miura VS consider going down 2 sizes IMHO. I also couldn't imagine the Miura 0.5 sizes down but hey, I don't climb as hard as you so if it works it works. Some people just complain about the Miura VS period btw and it may or may not fit your foot well.