According to the current and latest Nosler manual number 8, the max 250 gr in the 358 Norma Mag is 2628 fps with 72 gr of IMR 4350 and the max 250 gr in the 35 Whelan is 2637 fps with 58 gr of W748. In the 225 gr category it does show the 358 Norma with a 73 fps advantage.
Arrive at your own conclusion as to what you personally prefer. Looks as thoug the Whelan has the nod to me. I have a custom 338 06 built in 1984 on a Sako action, a toss up between that and a 338 Win Mag, after considering the pros and cons, for me it was a simple solution, less powder and much less recoil and not having to deAl with reloading a magnum case. Gave up 200 plus fps, but it a good choice for me. One trip to Africa, and 6x7 elk in British Columbia proved it does what it was meant to do.