no experience with the STW. I think the 264 is overbore as it is. I reached a plateau, where it just leveled off no matter what. It shot the 100hp sierra bullets very well. My father in law has 5 different .264WM, needless to say, if someone puts a new model out in a .264WM, he has to have it. every one of them likes 70.0 of H4831SC, with the 100hp. some like it better than others. thats all he uses deer hunting. That is now kind of a starting load for every one we get now. I liked the 120spt best to hunt with, although I have killed plenty of deer with the 100's. I did shoot an elk cow with my last WM, with the 120spt sierra, at 298yds. she went about 20yds, then rolled about 30 yds down a hill. at the butcher, when nothing was left but carcus, quartered up hanging weight was 346 lbs. My uncles 6x6 only weighed 30lbs or so more. the 100hp bullets in the 6.5-284 i had shot about 300-500fps or so slower, but I also didn't push them beyond max loads like some folks do. The 100hp did much better on deer when they were slowed down some, "better" meaning less meat & internal damage. I did shoot one elk cow with a (6.5-284) w/ a 140sbt, pass thru at 120yds or so. Same trip to TX shot a small bison with the (6.5-284) and the 160spt sierra. put it on it's butt right there. if you want penetration, shoot the 160's if you can find them. I shot the buff thru the shoulder, broke onside shoulder bone, directly thru the spine, and out the opposite shoulder bone. those are freaking big bones, and that bullet just left a huge hole thru all of them. the 160's will do very well in the 264wm too. you will love the .264WM. Yeah, I'm long winded. sorry. I think before I built another 6.5-284, I would compare it to the 6.5x55 swede.