If you can get a 225 grain bullet to 2850 fps out of your Whelen--at SAAMI pressure--I will eat the hat of your choice.
Look the Whelen is great, but it's not within 100 fps unless you're comparing the hottest .35 handloads with the most mediocre of factory .338 offerings. It's a simple matter of case capacity.
Does that mean the Whelen is crap? God no, it's a fantastic cartridge. But if you're guiding and looking for the occasional 300+ yard shot, then even Townsend would reach for the Alaskan.
Listen, Im not going to get into a BS ballistic comparison, but judging from your post, we're on the same page... Some loads are allmost Identical with 250's (velocity wise) less than 100 FPS difference, and some as high as 265FPS... BTW, I dont get 2850 FPS out of my 24 inch barrel in front of 225 gr X's... Yet, its not above max.
point is, the 338 is .020 smaller, and the 358 comes in the same bullet weights that the 338 comes in... The 338 win mag has a bit more powder capacity, but the 35 whelan is much more efficient...
YOu can go back and forth all day, but to call one a clear winner is literal BS... Nothing more than opinion, and favourites of each of us...
I personally love 35 caliber rifles, but dont own one right now... I have a 338 win mag though, and Im not parting with it thank you.
BTW, you shouldnt be taking the occasional 3-400 yard shot if your not brused up on shooting that distance... With a shooter comfortable with their tool, and caliber, they should be able to make the shot whether it be a 35 whelan, or a 338 win mag...
If we're talking hail mary, neither is a good option...
I just wanted to add in light of NWT's post that the 338 does have an advantage of being chambered in more rifles than the 35 Whelan (or any other 35 for that matter)
But this isnt enough for me to make something better. Just more available.