Here's my take on it. You didn't ask about Kimber Montanas, but a Montana in .308 is what I'd be looking at, and it's still a little lighter than an Ascent in '06. I've owned a few Montanas and handled an Ascent. I just didn't like the feel of the Ascent, plus you're stuck with a muzzle brake if you get one. The Montana just felt more solid, and as far as the trade-off between light weight for carrying vs. more recoil, 5 lbs. and change for a .308 is about my cut-off. I just don't see a need to go lighter than that, especially with a chambering that'll have more recoil than a .308. It just gets to the point where it's bordering on unpleasant to shoot much at the range.
I'd go Montana in .308 (or 7-08), for the following reasons:
1) Looking at the MSRP, you can get a new Montana, shoot out the barrel or just decide to have it re-barreled with a premium after-market barrel and pay the same as an Ascent.
2) I hate loudeners and lengtheners (muzzle brakes).
3) You already have a lightweight 300 WSM, a lightweight '06 doesn't get you much that's different.
4) For practical hunting purposes, a .308 will do what the '06 will.
PS, if you've made up your mind on the Ascent and are worried about ammo availability, get a .270.
I agree with your observations about the Ascent. It just felt like a toy. It actually kind of rattled when I held it. I don't know if it actually made a sound or if just felt like it but the combination of the fluted bolt and the extractor with cutouts in it gave the perception of rattling. And it didn't balance well either.
