I can say that I have chronographed 200 grain factory loads from the 338 Federal,35 Whelen,and 350 Remington mag.
The difference was pretty much negligible,the Whelen and Federal were virtually idetical,and the 350 was about 100fps faster.
This is due to the 338 Federal being loaded to higher pressures than the factory Whelen.
I can't really tell them apart in the field. Although full power handloads would give the whelen and 350 a 100-200 fps advatage with all bullet weights. We know this to be true because this is how a 308 sized case compares to a 30-06 sized case.
In the real world,they are the same.
