the Browning A-Bolt Mountain Ti and the Remington 700 Titanium are the only super-lightweight rifles ive actually handled, and between those the Browning was by far the nicer of the two. the problem is that the Browning is only chambered in WSM calibers. the Remington 700 Titanium in .308 is only 5 1/4lbs, and 5 1/2 for the .30-06.
the 700 Alaskan Ti in .300 Win Mag seems pretty cool, but its still a push feed and creeping up to 6 1/4lbs, at which point i dont see the point of shelling out over $2200 for a titanium rifle.
in the end i suppose it would be the Remington Ti in .308 at 5 1/4lbs, with quality aluminum weaver rings/bases and a light scope.
ive never taken a shot at anything other than varmints at 400 yards though, so i wouldnt be too confident with a .308 or even .30-06 at that range, id be much happier with a .300 Win Mag but they dont offer them in the 700 Ti. as much as i dislike them perhaps a short mag in the Browning Ti would be the answer?