Welcome to the site. There is lots of great info and help here.
I presently shoot a 300wby for long range hunting and hope to get a 800 to 1000yd shot at a buck in the coming weeks. My rifle is based on a 1 in 12 Douglas heavy barrel and muzzle brake
. It has the standard Wby chamber but I found that this shoots very well. Of course, the shorter throat would shoot well too.
I have used 165, 168 and 155gr bullets from Nosler (168 J4 and 165 Ballistic tip), Hornady Amax (168 and 155). I have settled on moly coated 155gr Amax over H4831SC, lit by a Fed 215M primer, in neck sized (Lee Collet die) weatherby and Rem 7STW brass. Muzzle vel is 3250fps and will shoot consistently under MOA at long range. Have now shot this combo to 1800m (1960yds).
There are many who have used the 308 Baer for 1000yd BR. This is an improved Wby and very close to a 30/8mm Rem Mag or 30/7STW. Accuracy and power is there for deer out to 1000yds. The reg. wby works well enough.
Key is making sure that your combo will shoot accurately that far from hunting positions or portable benches. Good optics are a must and most will recommend a scope with repeatable target turrents. You will need about 25min. of elevation to get from 100yds to 1000yds.
Read old posts to get an idea of the support equipment you should have in order to do this well. Laser rangefinder and good binos are a min.
If you lean towards heavier bullets, I would suggest the 190 to 220gr MK. I think the 240 is a little too heavy for this case. Try to get at least 3000fps accurately from your set up. The faster the better.
Try to use the longest barrel practical. Some have rigs with 36" barrels. Most of us build our rifles for the bench. Pretty hard to take an accurate 1000yd shot leaning up against a tree.