From my research the 338/06 carries a little better at long range when compared to the 35 whelen. the biggest bonus, if you handload, is the increased selection of bullets vs the 358's. the downside... very scarce factory ammo... i believe weatherby is loading for this or Norma or someone... On the other hand Remington offers 35 Whelen but i am pretty sure neither round is generally "stocked", even cabelas in Dundee, Mi does not carry 35 Whelen ammo.. and a very small selection of .358 bullets...
I did go the 35 whelen improved route in my latest creation because well i figured it'd be easier to find ammunition if i happened to be somewhere and lost of forgot my handloads... and the IMP verion can shoot factory ammo fairly accurately... If need be...
personally my 35 whelen AI.. pushing 250 gr bullets... with 53 gr of Reloader 15 has a MUCH more gentle recoil than my 280 remington loaded middle of the road with 175's...
i do sometimes think i should have gone 338/06 AI... oh well... if i ever really want to go for the gusto i'll turn the 35 Whelen AI into a Brown-Whelen or something
JR