Other than you are a one gun man with a bigger caliber, why would you ever feel the need to use anything bigger than a .243 Win for whitetail?
Because .30/30s are easy to carry and fun to shoot?
Actually, I switched to .270s a long time ago, because my .243 experiences weren't good (maybe bad bullets?), but this spring I picked up a .30/30 to mess with, and plan on using it this fall.
Funny. I did the same thing. After years of killing an embarassingly huge amount of deer with anything from .223 to 300 Mags, I decided to play with a 30-30 for the first time ever.
The Op's question has a key word: "need". No, don't really "need" more than a .243. As said on here so many times before, bullets mean more than headstamps. .02" of bore also means a heck of a lot less than construction of the protjectile(.22 vs .24 for example), accompanied by velocity.
