A 9" twist 7mm mag will do just fine with the 168s and some of the 180's...it just depends on the load the rifle likes. My last 7mm Rem Mag ( 9 1/4" twist 26" bbl) shot the Sierra 175SBT super well, but it did not like the Nosler 175 ABLR ( which is a beautiful bullet too!) No biggy, that 175 Sierra has been knocking them down for decades. A 7mm mag "might" feel like a 300ma/180, it still has "less powder' in it. "Ejecta" is the term. In the field, you won't be able to tell the difference on elk...the 7mmmags are easier to shoot, and plenty of power, even for moose! I've had sporter weight 7mmmags that recoiled easier than lightweight 30-06s! I do believe for prone ( assuming no brake used for either) you are miles ahead with the 7mmMag. My SIL uses a Tikka T3 Lite as his lightweight, knockabout elk rifle. It shoots the HSM ammo with 168 Bergers like match loads. His last elk was popped around 325yds, down he went. He popped him again as with elk "its best to keep shooting until all the wiggle is out of them"! Both rounds fully penetrated too, golf ball sized exits...perfect. ha. I had to go to a muzzle brake years back due to a neck and later an eye problem ( i.e. I only have one good eye left, gotta protect it, ha) So I can shoot some heavy hitters ( big mediums like the 35 Whelan AI, 338mag, 340, 338 RUM, now my 358 Norma) I don't "need" any of them for elk, but they will 'chill their do doo" pronto, ha. Good luck to you, and don't look back from that 7mm mag...just shoot the devil out of it, get really good, and take a camera with you for pictures!