For a factory rifle I would get a Rem 700 in the 300 RUM shooting the 200 gr Accubond.
Personally as a custom rifle
maker, I would not be real confident in your chances of getting a factory rifle to be accurate enough for engaging big game at 700 yards. 500 possibly with top loads.
I guess I am a sceptic from all the factory rifles I have torn apart and witnessed how they were put together.
If it were me, I would get a Rem 700 action. Fully and properly blue-print it and fit it with a 28 to 30" #6 Lilja stainless barrel if you are hunting in open country.
If you are hunting in cover I would go with the standard 27" or possibly better yet 26" with the same Lilja barrel.
The #6 contour offers plenty of stiffness for great accuracy and still is light enough to carry in the hills. It will not make an ultra light rifle by any means, probably in the 9.5 lb range but 700 yard shooting is not for light weight rifles.
Optics wise, I would select the 4.5-14 Weaver Tactical. This scope has the Mil-dot reticle that is on the first focal plain. This allow the power to be adjusted and the spacing onthe mils stays consistant and accurate though out the power range. This is a feature more US optics makers need to follow up on.
This scope is also extremely clear and reliable for the money. I have tested then side by side with $800 and $900 Leupolds and the Weaver is noticably clearer to my eyes and at least as accuracy, rugged and consistant.
I have one of these on my wifes 257 STW. Loded with the 130 gr Wildcat Bonded Core FBHP at 3500 fps and sighted in +2.4" at 100 yards, there is no need to adjust your hold out to 400 yards.
At 450 and 500 yards you just hold on the first dot below the main cross hair.
At 600 yards, bullet impact is within 1" of your poitn of aim.
For 550 yards you have to hold half way between the dots which may sound like guessing but bracketing an animal between two mil dots makes for precise hold.
Again, if its dark youcan turn the power down to 4.5 power and the mil dot system is the same.
For long range shooting, turn it up to 14x and still your set up to use the reticle to its full potential.
This is perhaps the best scope I have found for big game hunting out to 800 yards.
For longer shots it lacks a little optical power but for anything inside the half mile mark, it is a top notch system
Being able to engage any target from the muzzle out to 800 yards without ever having to dial in the clicks is perfect for big game hunting.
Its fast, accurate and very consistant and you never have to worry about loosing your click postion inthe field in the excitement of the hunt.