My 600 yard Elk rifle is a Model 70 Classic SS BOSS. It's in 30'06 and out of the box at initial factory settings and grabbing my 'usual' handload for 180grners shoots 5/8-3/4" groups. What more do you need? Heavy, long barrels are needed when you want to shoot alot, but for hunting you only need 1-3 shots before the barrel heats up. BTW....7.5lbs with scope is light, not 9.5 or 10lbs.
Carry your bipod in your ruksack.
With practice and high BC bullets an '06 is plenty for Elk--despite all the hype. The use of 7mm or 300 RUM cracks me up. 1,000 yrd target guys moved away from that heavy artillery long time ago. Burning 100grns of powder every time you pull the trigger assaults my sense of frugality. Granted, animals require more energy to nail than paper, but a 180 class bullet launched at around 2,800fps is attainable and will do the job. Will also allow a heck of a lot more than 1,000 rounds for barrel life. I don't even want to think about the recoil of an RUM in a 7.5lb set up--even with a muzzle brake.
If you want something sexy, go for the 280 AI and either a 3.5-10 or a 4.5-14 AO scope. Personally, I'm not really worried about paralax. At 500yrds is only 2". Get a scope from Leupold and have them set the paralax at 300 yrds. On an Elk 10x at 600yds is plenty--afterall, you're not trying to count the hairs on his rump! A 3.5-10 x 40mm weighs just 13oz. The big scopes run 20oz and up.
I had a rille in 280 AI and handloaded for it. Is a great cartridge. Loved the gun. My rig ran 7lbs loaded. This cartridge shoots well with long case life, little recoil and very flat trajectory. But, you gots to handload. Between a 280AI and and '06 I'd go for the 280AI. That just because I'm sexy. Try out 160 grainers as well as the 175s.