A 1-12 may be marginal for a couple of the bullets you mention at your elevations, but I can assure you it is not in Montana, even at the lowest elevations of a little over 2000 feet above sea level in the eastern part of the state. Have used all the lead-free bullets you mention, plus the plastic-tipped 39 and 40 lead-cores, and they've grouped very well in all the 1-12 twist .204's I've used. My varminting buddies tend to prefer the 40 V-Max for all .204 shooting here, partly because it groups so well, and all their rifles have 1-12 barrels as well.
The JBM Ballistics bullet stability program, which unlike many twist programs accounts for plastic tips, indicates both the 32 Nosler Lead-Free and 40 V-Max are well-stabilized by a 1-12 twist in typical rodent-shooting conditions here.
