An SKS can take a good sized deer at close range with proper bullet placement.
My old room-mate used one for years and harvested every deer he shot at, but I can't remember any shots past 50yrds.
While the 7.62x39 and 30-30 look similar on paper, the big difference in knock-down power is the cross-sectional size of the bullet, the 30-30 hits way harder, and creates a much more damage tearing thru the animimal because of its fatter bullet.