#5 go kill an Elk with .223 and 77gr TMK, might limit you to 300 yards thoughHere is some free advice.
You need to fix the primary source of your issues: yourself. Dropping down to a 6.5 will not resolve your issues.
Here's what I personally would have you do:
1) Take a training class with a real person, preferably one on one, and get any flaws and/or bad habits in your shooting process eliminated. This class should solely focused on shooting fundamentals and NOT on long range shooting.
2) Buy another T3X in 223 and practice what the class taught you; muscle memory will make things easier overall. Practice your fundamentals. Practice your shooting process. Practice shooting in the wind. Practice reading the wind. Practice Kraft drills. You get the point.
3) Take a long range shooting class with a real person. Depending on what they require, you may need to do #4 ahead of time.
4) Re-evaluate whether the 300 WSM makes sense for you. If it does, look at getting hand-loads developed for it so that you can get more consistency.