Lawdog, I am a Maine Redneck, well not really I grew up in a ritzy and liberal town in Connecticut but I went to collage up here thus I ain't so good at the PM stuff if you want my Email address is theworkshop@tds.net.
The reason I went with the Rigby necked to 9.3 or .366 diameter is that it is legal in many areas of Africa for dangerous game. Also .366 bullets have very good BC and sectional density, meaning flat shooting and great penetration. Originally I too was thinking of a .358 but with the advantages of legality for African dangerous game and bullet construction offered by the .366 I went with that diameter. .008 difference does not make much difference. A .358 Rigby would be devastating but you would have to be really careful with bullet selection. For example a 200 grain bullet designed for the 35 Remington and meant to expand at 1800 FPS, you could push at around 3400 FPS. This is what is the true meaning of bullet failure!!!!! The 270 grain Speer in 9.3 though incredible accurate verge on this when used on game and fired from the .366DGW. Bye the way if you want more info on the .366 DGW either look on page 201 of the tenth edition of Cartridges Of The world or give me a call at 207-938-3595