The lightest .308� LRX is 175g so �lighter-for-cal bullet� would mean a TTSX in the 130g to 168g range if keeping the bullet design as similar as possible.
The OP's question was not limited to Barnes bullets.
To answer the OP's question, what's the twist rate on your barrel? It may be twisted such that it won't stabilize the heavier bullets. And there's no need for 200's or 180's anyway; if you're going to shoot the rifle much, do yourself a favor and go with 165's or 150's.
Shoots my hand loaded 165 speer deer loads .5 moa to 400. Also shoots factory cheap 150gr federal .75 moa. So I know the gun shoots and nothing else is amiss. It's just that I wouldn't want to use either on elk hunting.
I can't follow your logic here in not wanting to hunt with a .30 caliber 150 or 165 at a higher velocity than a 6.5 127-grain bullet. The 150 or 165 will do fine on elk.
If I were in your shoes, I'd use the bullets that shoot well or if you don't want to use those pick a few different bullets in that range and see if you can get them to shoot in the WSM. No harm in doing that.
But elk season is getting close, so if you don't find a good combo for the WSM, hunt with the LRX and don't look back. Confidence in your shot placement is worth more than anything else. Shot placement is the most important thing, followed by bullet construction, then headstamp. The crappiest bullet (I'm not saying the LRX is crappy) will succeed with good shot placement.
As far as the LRX failing to open up, you could hunt for years and not have it happen to you. That was not my point.
The only reason I brought up the fact that monometals sometimes fail to open was the blanket statement by someone who's never used the bullet that there is no situation where the bullet wouldn't be as good as another bullet.
As with most sweeping all-inclusive statements, it's just not true.
