How does the STW hold up to the .300 WM? I think you mean, "Does the .300 WM even hold up to the STW?"
I think it's a better caliber, personally. But alot of people will always argue that. It will turn into another Rem vs Savage feces-fling...
Here's what it comes down to... 7mm STW is the king of the 7mm's. BECAUSE it is the largest step in the 7mm calibers that you can go, without major diminishing returns. In other words, you won't be pumping 20 more grains of powder just to get 50 more fps... Such as the case of 7mm STW vs 7mm RUM. Plus, the STW has a significantly better better life than the RUM (known fact). Just things like that.
As for 7mm STW vs .300 WM..... They're close, but I still say the STW is better, simply because I am a bigger 7mm fan than I am a .30 caliber fan, although I do own quite a number of .30 caliber rifles, including the monster .300 Ackley.
Now if you said .300 WM vs .300 Ackley..........300 Ackley all day long. There's people loading up 80+ grains of 7828 in a .300 Ackley with 200-220gr bullets....That's MOVING. I haven't worked mine up that high yet. I've found a good node around 74gr, but I'm gonna see if I can find another one and see how fast I can get my 210 Bergers...