You can chamber the 338 Edge in a Rem 700 action and set it up to handle a 3.9" COAL... Easily.... And get 2800 to 2850 FPS with 300 grain SMKs
The 338 Edge is the 300 RUM necked up as has already been mentioned and will hold about 6 to 8 grains more powder than the 338 RUM does.....
range it,check the wind, dial in correction, aim and only one shot
If you are going to shoot the 300gr SMKs, then I would get the 338/378. I have one of these and it is extremely accurate.
If you are going to shoot the 225 Nosler Accubonds, then I would ge the 338 RUM. I also have one of these and am very impressed with the caliber. Get some H1000 and a 5-1/2 foot drop tube and filler her up.
Finally, I will mention the 338 Lapua. I also have one of these in the standard and the improved version. For what it is worth, I would choose the 338RUM over either of these as the gain is not very much with the heavier bullets and it is a dead heat with the 225 Accubonds.
My 338 RUM was a project that had limitations on the magazine length since it was a vintage custom repeater action. Anyway, it equals the 338 lapua in velocity with the 225 accubonds and has a slight edge in accuracy.