I wouldn't worry too much man, it's the middle of July so I doubt you're gonna be riding on em soon anyway. I ordered some s/m 390s for my size 9 ride anthem boots and they ended up being too small.
Shipped em back for free and got the l/xl bindings two days later. They fit perfectly.
I'm actually in Australia so it's currently part of our very short snow season.
It also makes the shipping/returning thing tricky as they are coming from the USA. It is possible if I get onto it before they leave the USA it will cost me a bit of money/time but I'd rather that than bindings that don't fit.
I have size 9.5 Burton Hails with shrinkage as well. And yes, your boots have shrinkage. I went with the L/XL Rome 390 bosses. I had issues initially, but have since solved them. If I could redo my sizing choice, I would have went with the S/M.
Burton's shrinkage tech really does what it's supposed to. Just max out your settings on the bindings. Make sure the ladders for your toe straps are set in the forward position. Move the heelcup to the correct position for 9.5.
Glad you noticed this post as it was some of your other posts that really got me thinking.
I have to say I'm surprised by your answer I was pretty sure you would recommend the L/XL from your previous posts. I appreciate your honesty on the matter though.
Could I ask you to expand why you would go S/M next time rather than the L/XL considering with adjustments you got the L/XL fitting well? What do you find lacking in the L/XL.
A point I read of yours in another post was what happens if my next pair of boots don't have shrinkage which I thought was a good point.
Did you have to switch any parts i.e shorter straps etc?
I actually just received a reply from Rome email support and interestingly they recommend the L/XL to play it safe.
My S/M are currently in transit but I can still do a last minute swap it will just cost me some time/money.