Personally for me, a big part of having a special hunt is using a cartridge that appeals to me and one that I enjoy using.
There may be several cartridges available that would be up to a certain task I ask of it, but some just appeal to me more than others.
That of course doesn't mean that the other cartridges aren't suitable, I just have my preferences...
So I would personally choose the .300WM over the 35 Whelen.
I have owned 3 .300WM's, plus a .300Wby and a .308Norma and really liked them all. I'm just a massive fan of .30 Magnums
Of the over 50 rifles I own or have owned, I have never owned a 35 Whelen - but I have owned a couple of Winchester M70's in .338WM, which I prefer.
Nothing against the 35 Whelen, it's just a cartridge that has never personally appealed to me... that doesn't of course mean it isn't any good. Like I said earlier, I just have my preferences...
So I would choose the cartridge that you would prefer to hunt with and take that... taking a favourite rifle/ cartridge on a special hunt will make it just so much more memorable...
Just my 0.02c
Russ