The 338 Allen Magnum is much larger then the 338 Edge. It is based off the huge 408 Chey Tac parent case. Typical performance levels are in the 3300 to 3400 fps range with 300 grain SMK or 3500 fps class with some of the 265 to 275 gr custom aluminum tipped bullets.
Its in a totally different class of performance then the Edge but that does not mean its best for your needs. Just depends on what you are planning on doing with your rifle. The main difference between the two is performance numbers and barrel life. That said, if you take good care of a 338 AM barrel, it will last you many, many seasons of hunting big game at very long range.
Left to right, 338 Edge, 338 Lapua, 338 Allen Xpress and 338 Allen Magnum with 265 gr AT RBBT.
Hope this helps.