New Barrel Decisions

I’ve ordered a barrel from Preferred Barrel Blanks about 2 weeks ago but I am second-guessing my decisions for twist rate, length, and chamber dimensions. I have a handful of questions that I would love some help with.

Background: I have a Ruger American predator gen 1 in .308 that I have slowly been modifying over the years. This is the poor mans solution. Just start with a cheap reliable gun and slowly make it better. I started reloading when I purchased the gun and have really enjoyed the whole process. I want to make it a crossover between a hunting rifle / precision long-ish range. Over the years I have replaced everything besides the action and the barrel, and currently I get about 1.5" groups on average at 100 yards. I want it to be better in the average .75" groups range.

Current barrel: Stock 18" ruger american predator barrel 1-10 twist

New barrel I ordered:
Length: 20"
Profile: Medium Palma - Seemed to be a profile that was light enough, but still had enough metal behind it to not heat up super quick.
Twist: 1-12 - I want it to shoot lighter bullets better. Current 1-10 twist rifle does not shoot 150’s or lower well at all.
Chamber: Alpha munitions reamer - They have a SAAMI, and a Match chamber reamer as well. The alpha seemed to be the in-between sized one. I still want to be able to shoot pretty much any cartridge I want. I just want it to be a more modern, accurate and tighter fit than SAAMI, but I may be wrong.

I guess my question is, based on the background, my goals etc… would you talk me out of any of the above decisions on the new barrel? If so, I would love to get some of the reasoning behind it. I think I still have some time to shift

I don’t think I’d change anything on that barrell. 1:12 is common, 20” will get you slightly better velocity, and medium palms is a good choice. That’s a winner.

@backfire thanks for your reply. You have mentioned in a few video’s that you believe more modern cartridges seem to be more accurate than say the .308 because of the 1) tighter tolerances in the SAAMI spec? and 2) Allowing for longer BC bullets. Do you think getting the chamber cut with a more modern dimensions could help with that? Hence me deciding to go with the alpha munitions reamer instead of the standard SAAMI reamer…

The alpha munitions reamer seems to be slightly tighter on the neck, and allow for longer bullets