Hodgdon shows top speeds for 200s in the 06 to be about 2600fps-2700. Hodgdon data selection is small ut most 35 wheelen loads beat that by 50fps, with one hitting 2800. The loads for the 250s run slightly faster than 2500.
I dont disagree on penetration or down range performance tho.
Still if nothing else the .35s are cool, and the extra 20-50grns of bullet weight are appealing to me.
I looked at my Hodgdon loading manual and the 300 Win Mag is operating at 4,000 psia above the 35 Whelen. None of the 35 Whelen loads exceed 50,000 cup, all the 300 Win Mag loads do. Of course with higher pressure, you can push a bullet faster. However the 300 Win Mag sort of peaks out at 220 grain bullets, the 35 Whelen is just getting started. The 220 to 225 grain bullet is a good "mid range" bullet, the cartridge was originally designed with a 250 as the base. Col Whelen wanted a 250 grain bullet at 2500 fps. In days past, it was common to use 275 grain bullets. These bullets are no longer on the market. As Townsend Whelen says in his 1920's American Rifleman article: "
As a result we standardized on the load for the 200 grain bullet at 60 grains of Du Pont IMR Powder No 6, giving a muzzle velocity of 2834 fps.......For the 250 grain bullet we standardized on the charge of 62 grains of Dupont IMR No 45 giving a muzzle velocity of 2635 fps. " Obviously the loads back in those days were a bit more stout than what the manuals allow now. I have to believe that a 250 grain bullet moving at 2635 fps would be a very powerful thing indeed, on both ends!
The guys at http Accurate Reloading.com
http://forums.accuratereloading.com/groupee are not only very positive about the 35 Whelen, they are also fans of the 9.3 mm cartridges
https://en.wikipedia.org/wiki/9.3×62mm which use a .366 diameter bullets. Lots of words have flown whether the 35 Whelen is a better game getter than 9.3 X 62 mm. The only real consensus is that a .366 cartridge can take even heavier bullets than a 358 cartridge.
As to whether the 300 Win Mag "hits harder" than a 358 Whelen, that is a topic well fitted for hundreds of psuedo science posts. I also have not seen any calibrated test data showing that one penetrates better than another.
What I can say, is that fitting a 300 Win Mag cartridge to a bolt face already cut for a 270 Winchester is going to be a lot of work. And regardless of the feelings about the superiority of belted magnums, I would not recommend this cartridge conversion on an existing action not already set up for belted magnums.
The 35 Whelen is an excellent cartridge, as Townsend Whelen wrote "
While the 35 Whelen is not a world beater in any single respect, yet when it comes to that most to be desired combination of killing power, accuracy, flat trajectory, reliability, there is not another cartridge which can stand up against it for a minute." That was written in the early 1920's, well before the Weatherby magnums, but the cartridge is still an excellent round which is why it is still around.