BFJ:
I have no experience with jumbo, and would probably caution against using the .577 N-for-B load on the big pachyderms today when so many alternative cartridges are available. Nevertheless, here are a few observations to mull over:

Using a steel-jacketed solid of 650gr at 1665 fps (specifically, the Woodleigh solid for the .577 x 2 3/4 NE) for the frontal brain-shot on ele, we have a Taylor Knock-out Value of over 90.

This quote from 'Pondoro' Taylor's published work 'Big Game and Big Game Rifles', although somewhat controversial, should help put that into perspective:

"Any rifle which shows a KO value of not less than 50 can safely be relied upon to knock down an elephant in any circumstances, though it may not stun him. Over 60 values are necessary if he is to be stunned and not temporarily dazed."

The .577 Light Nitro load would be looking pretty damn good even as an elephant-cartridge according to Taylor!

Regardless of your opinion of the above sentiment, it is unarguably a damn fine buffalo cartridge!

Here's a link to my opinion of the .577 Light Nitro as a modern DR chambering, for new-comers who haven't seen it before.

After all that, the .400 NE needs no soul-searching, it just plain works!