Get the Remington. It sucks you can't do the Sendero, but you should be able to make the SPS work. A good bedding job, a good trigger, and a good crown and you should be good to go. Most Remigtons will shoot...eventually if not right out of the box. Good choice to go with the 300WM it's a great round. My buddy and I shoot Ultra Mags, but honestly as long as it is accurate and you can put a quality bullet precisely where you want it to go, any of the flatter shooting cartridges work great. I didn't catch if you reload or not. If not, spend money and time there first. You will by far get the bigges bang for your buck. You can adjust the X trigger. Do a search and there is lots of direction on this site and the web, just make sure you have enough sear engagement to keep the trigger from tripping when you close the bolt hard, take off the safety, etc. I don't know anything about the scope you talked about, but this will definitely make or break your long range success. There is nothing that will waste more time, money, or a nice day than a scope that isn't repeatable and reliable. OK maybe a bad round of golf, but not much else. When choosing a scope, remember that this is going to be a heavy recoiling rifle and you are going to be using all of the adjustments on the scope, so it has to be quality. I'm not saying that Leupold, Nightforce, or USOptic are the only choices out there, but choose wisely, spend what you can afford the first time, and don't look back.
Welcome to the sport/hobby/addiction and enjoy the ride. If you have the opportunity to shoot at extended ranges, you will learn more about shooting in the first 100 rounds at long range than you have learned in years of shooting 100 yard groups. Even if you never take an animal at 1K+ you will become such a better shot at 500 and in. Best of luck and if you can afford to do it right the first time, do it.
