I have a Sendero SFII in 300 RUM and I really like it.
My best load to date with 200 Accubonds averaged 1.6" for five, five shot groups at 200yds.
My best load to date with 165 Accubonds averaged 1.2" for four, 3 shot groups at 200 yards. Note, these are averages of several consecutive groups, not a one-time best group. Those numbers are quite good in my books. Incidentally, the 165 Ballistic Tip was indistinguishable from the AB when substituted.
I had some trouble getting it to group well when it was new, I don't know if the barrel needed some rounds through it or what but it groups well now and fouls very little.
I did skim bed it and added a Timney trigger along the way.
Scope is a Leupold 4.5 - 14 x 40 (B&C) (Highly recommended)
harder to find ammo/brass
higher priced ammo/brass
shorter barrel life/more barrel heat
heavier recoil
more muzzle blast
the extra 10% in velocity comes at a cost of 25% more powder burned. Since a 300wm already will push a 180gr fast enough to reach 600 yards with authority, I see little practical use of the larger cartridges. Successful long range shooting is decided by the shooter, not the fastest baddest cartridge
my .02
All of the above is true and if those factors are a concern the 300 WM might be a better choice, but with 300 RUM:
The case neck isn't too short
It has no stupid belt
It has little enough case taper that case stretching isn't a big problem
The Sendero is heavy, which helps with the recoil
The Sendero has a heavy barrel, which helps with the heating
There isn't much out there that will shoot flatter with less wind deflection than a max 165 grain load with a decent BC, check it out.
The 200 grain load shoots very flat as well with a little less wind deflection and delivers some very serious momentum at long range. That's pretty cool.
I really like the 300 RUM in the Sendero.
My next plan for this rifle is to try some Federal 210M primers instead of WLRM's in my current loads and to try some new loads with other powders.
When I wear out the barrel I'll have a perfect excuse to get a match grade barrel installed.