As to the Max OD, there's a long Sako video (Complete Story of Sako S20) that talks about an insert you can remove to run a larger Dia. barrel like a carbon option, they said it would be fine to run without the insert. However I don't think they mentioned a max size. They also mentioned that different size inserts would be available down the road. Not sure why, if it's a free floating barrel, perhaps the inserts just add chassis rigidity. Of course that video was done 7 months ago and also talked about ARCA plates, and I've yet to see either anywhere.
I was able to handle both versions in short/long actions at Cabela's a couple weeks ago, I still have very mixed feelings about it. The actions were smooth, but not TRG smooth. The trigger was nice, but I'd rather have the 2 stage. I really want to like it because I love my TRG, but it's a hard sell.
I wish it had a full length pic rail, and 20 MOA while at it, It's too far between them to run any of the one piece mounts, and the sako S20 mount is vaporware, especially if you want the 20MOA. Which is the next biggest issue with the S20, can't get the 2 stage trigger, can't get the heavy profile barrel, can't get mags, can't get half of the S20 parts and the rifle has been in stores for almost a year now. As Lowlight has said dealing with Sako/Beretta is just painful. Having the mag release built into the magazine....not sure how I feel about it, it's intuitive, but you have to get the right angles on the mag going in, you can't just slam it in there. Also the mags in 300wm are really bulky. I do really like that it appears all the fasteners I saw were probably like T20 or T25 across the gun, instead of 5 different bit sizes.
As so many others have said I was not impressed with the feel of the stock at all, very cheap feeling plastic and the display models had a lot of dents/scratches, tapping on the plastic isn't like tapping on say AI or KRG side plates, instead it's very hollow thin sounding. Sako says it's a "rubberized leatherlike gripping surface" on the precision version but it's just slick hard plastic, slightly textured at the grip. The hunting version has a couple small rubber like inserts at the grip and forearm. The cheek adjustment felt very iffy and was hard to adjust both up and down. The LOP on the precision stock was super long, no way I could get proper trigger position without sliding my hand way around the grip and I'm 5-11. Looked like there was 2 thin spacers you can remove and the trigger moves a bit, but it's still way too long. The hunting stock was better, or at least felt that way. I also thought the balance of the hunter setup was better, but that might change with an optic.
Add to that we've seen a few video reviews where the rifle did not impressive from an accuracy standpoint, and the fact getting accessories/parts seems basically impossible, and we still can't get a 2 stage trigger or heavy barrel here it seems like sort of a let down.