I went through this same decision making process. Some comments:

1. You can get a Searcy in 577 for $15K, or a .500 or .470 for $9500. www.searcyent.com As for the 450-400, it is a good caliber for double fans who have gotten too old to take normal recoil. (Am I going to get hate mail for this?)

2. A .577 weighs over 13 pounds, while a .500 weighs 10.5 pounds. After an 8-12 mile fast-paced stalk in Africa at 100 degrees, the extra weight is difficult to deal with. At the shooting range, the weight does not matter.

3. If you want a really big bore, try this 700 NE for only $35K:

http://www.gunsamerica.com/guns/976473654.htm