The Whelen is a lot more cartridge than the .35 Rem. With an uber load, the Rem will push a 200grn pill somewhere around 2300, factory fodder will be around 2050-2100. The Whelen will push the same 200grn pill up over 2800 with a smile on its face. A lot more powder, a lot more recoil... fantastic cartridges in their own rights, however, both of them. Just different weight classes.
Don't count out your 44mag in a conversation about the .35 Remington. Getting a 240 up over 1600fps isn't a challenge, even 1750 can be within reach. The 240 XTP has a BC just over .2, most of the blunt 200 grn pills for the .35 Rem aren't much, if any better, and again - you're only talking 2100-ish feet per second. I shoot .44mags out to 250-300 fairly regularly, my 250yrd hold is the bottom edge of my 1st mil-dot. 250 with a .35 Rem would be just a touch over half a mil. Not a big enough difference for me to buy a new rifle over - especially when the .44mag is cheaper for factory ammo (and more widely available), and uses less than half of the powder of the .35rem.
Don't let that discourage you from buying a new rifle if you want one - as the .35 Rem is a great round, but I also wouldn't want a guy to buy a new rifle thinking it would change their world compared to their owned rifle, without really feeling out what the real differences might be.