I do nto have a 35 W Handi, but I do have a Mauser '98 Bolt gun.
I have found that both 2520 and RL15 are top preforming powders. My all time favorite bullet is the Speer 250 Grand Slam, but the 250 Hornady RN and if lighter the 200G Spitzer are very good and cheaper.
The Whelen really begins to shine with the heavier bullets and that 250 GS bullet is a great one! Smashes thru and breaks down the biggest game. Try it with RL15! Dont worry one bit about RN or protected point bullets at 250 yards. Altho they will be slightly slower, they will be just as accurate. most in the know say if under 300 yards bullet profile is of little consern.
Good lukc,
CW