1894,
If you get a fast barrel you may play with the 3450 to 3500 fps range with the 85/90 gr bullets but I feel you would be pushing things pretty hard.
If I remember correctly you said the area you will be hunting is pretty flat and it is relatively open as well, you will be better served with a longer barrel.
The big 6mm rounds really start to run hard with a 28" barrel. So if this would fit into your hunting style, you certainly woul dhave a better chance getting your velocity goals with a bit longer barrel.
THe big 6mm rounds are what they are and nothing else. If your building it to outperform your 6.5 round you may not be totally satisfied. A 25-06 AI or 6.5-06 AI will smoke the 6mm-06 in every catagory but they also generate more recoil.
For longer range shooting, you really need to get into the VLD bullet designs to see any real advantage with the 6mm over other similiar calibers like the 25 and 6.5.
If you get a 28" barrel and drive a 105 gr A-Max or 107 gr Sierra or better yet one of the big bonded core bullets that Richard Graves builds at Wildcat Bullets such as his 110 gr and 115 gr Flat base, then you will start to really get into some serious long range possibilities compared to the smaller bullets.
Even a 95 gr Ballistic Tip has a pretty low B.C. compared to these bullets which will run in the low to mid .500 range. They can really turn the big 6mm's into something special.
Still they are 6mm's and on game, while they are great for the smaller deer species, they are not overly powerful at ranges much past 400 yards. They get the job done fine with good shot placement which is always the goal for sure but it is much more critical with these rounds.
Good Shooting!!!
Kirby Allen(50)