If you want past 300 and reasonable and available factory loads look at .270. I have mine in a Win Model 70 with luep on top and my first 500 yd shot I ever took centered on a torso target. For a lower cost I would look at a savage. You should also consider reloading while you can sling 130 and 150gn rounds a long way I really like 90gn Sierras for the range and varmint.
As for the 17HMR I have taken lots of prairie dogs at or just past 200yds but that round is out of gas at that point. Inside 200 it's a ball and out to 150 it's a laser.
In either case look for good glass in the 6*9*40 range.