I just built a 35 Whelen on a mauser action, so I'm a whelen newbie, too.
I've tried 4 bullets, so far.  I tried the sierra 225g, with IMR 4064 and reloader 15.  Accuracy was getting there, but I can't find anymore of those bullets.
For a lighter load, I use remington 180g hollow point 357 handgun bullets, with surplus wc846 (like BL-C2), or with blue dot, for very light, quiet loads.
I've been trying 250g speer spitzers and hornady round nose.  With Reloader 15, I can't get anywhere near max wtihout pressure signs, accuracy not great.  I've got more to try next time with IMR 4064.
If anyone else has suggestions, I'm listening, too.