Back to the OP’s specific question:
With respect to your question on using the 0.416” 400 grain CEB Solid, I had a chance to shoot a medium size tuskless 2 years ago with a 404 Jeffery Win M-70 using the CEB BBW#13 0.423“ 400 gain FP Solid loaded with RL-17 to MV 2500 fps. A lateral heart shot at ~40 yds through the heart exited through the off shoulder. Almost the duplicate of michael458’s shot. Elephant went about 30 yards. Although this bullet is slightly larger in diameter than the 0.416” you’re considering using, the performance should be just about identical
In the 458 WM, I’ve settled on the CEB BBW #13 450 grain FP Solid you’ve cited, at 2400 fps MV with 2230 powder. That load has also shot through a tuskless in a setting almost identical to the 404J shot described above with the same results.
I use the 500 grain CEB BBW #13 in the larger volume cases of the 460 G&A and 450 Rigby Rimless. The former at 2400 fps and the latter at 2450 fps. I used the G&A last year on a tuskless. All bullets, starting with the initial frontal brain shot which dropped the animal at just over 35 yds, the subsequent insurance shots - side brain, frontal and lateral chest - exited.
As to the other question in the thread about the ballistic performance of the Barnes Banded Solid vs the CEB BBW #13, I’ve found that using the same powders and loads with each, at very similar COAL, the MVs are very close with Barnes, in my rifles (500 NE 3” DR, 450 Rigby Rimless), the Barnes seems to produce a very slightly higher MV.