Don't like to keep posting to this subject, but it is a calibre I really like - so.

Woodbeef, good choice - 12" will be fine for any bullet weight, but if you have the opportunity to use longer bullets, 280gr. pointed bullets or even heavier yet, it will probably provide an edge in accuracy.
The 300gr. bullets in .358 are quite 'special' RN or otherwise shaped.
For the heavier bullets, I'd probably go with an improved case and stick with the standard Whelen with 270's or lighter. In this one, a 14" is probably all that's really needed. My 9.3x57 has a 14" twist and puts 270gr. at 2,300fps as well as 286 @ 2,200fps and 300gr. at 2,175fps into 1-MOA groups at 100 meters. This calibre's bore diameter is the same as a .358" groove diameter, just as a .375 has a .366" bore diameter, normally. Only groove depth separates these three, in order.