I have a half dozen of the HS Stocks and love them. I have the old green ones, a tan one, and I just got a new one in black with red web. Beautiful stock.
I'm in Canada and have never seen any low temp affect. But I'm not shooting bench rest at -40, just coyotes and other varmints.
The basic bedding block in the HS looks like a perfect fit to the round action but it really isn't. If you use bedding transfer dye or tape, you will discover that it's a mild V-Block design that makes contact on a pseudo rail down both sides and also at the rear tang. ALL of mine are like that, or perhaps I should say were.... I have epoxy bedded all of them except the latest red web one. I'm fairly certain that I will end up bedding it too once I finish building the rifle. I am chambering it as I write this for a 222 summer varmint rifle. (I have one I re-painted in snow camo for this time of year).
I have found that the pseudo V-block bedding design is a bit temp sensitive. But I don't think it has anything to do with the difference between steel & aluminium expansion rates. While they do have different rates, I believe that wood or even bare synthetic would be much worse. While I do like laminated wood stocks and have several, there is not a snowballs chance in hell that I'd ever take any wood stock over an HS style stock with a bedding block regardless of temperature. Humidity is MUCH worse with wood. After bedding the block to a perfect action fit, they are all as stable as I can detect at any temperature I'm willing to shoot at the bench in.
Oh yes, for those who don't seem to know, 5R is a type of barrel rifling. (5 lands with Ramped edges) It's not a rifle model or type.
Last, but not least, I LOVE the HS palm swells. I am a big guy with big hands and the grip and feel of the HS is simply awesome in my eyes. But beauty is in the eye of the "holder" ... ... LOL!
Cheers!