My perspective is a bit tainted as I have never shot a deer with a .243 and calibres less that .243 are illegal for big game in Alberta.
The reason for choosing a larger calibre can be based upon the size of the deer one hopes to encounter and the nature of ones hunting. When the possibility of shooting a large deer at close range, with less than perfect presentation, possibly whilst it is running would justify a larger calibre and a heavier bullet.
Just my 2 cents and YMMV.
An early happy independence day to y'all in the great United States. GRF
