There are two issues at hand. One is energy. The other is momentum transfer.
Here are some muzzle energy for factory loads of the two rounds.
30-30 factory loads:
- 150 grain round - 2,390 fps - 1,902 ft. lbs energy
- 170 grain round - 2,200 fps - 1,827 ft. lbs energy
7mm factory loads:
- 140 grain round - 3,400 fps - 3,593 ft. lbs energy
- 160 grain round - 3,200 fps - 3,637 ft. lbs energy
The 7mm clearly has the uupper hand here. However, that energy needs to be delivered to the deer to be effective. Or more correctly, the momentum of the round needs to be transfered to the deer.
This is where, for example, hollow points are preferable to full metal jackets. The hollow point will cause the bullet to mushroom giving it better momentum transfer properties (and therefore knockdown power). FMJ rounds tend to go straight through causing somewhat less damage because of less momentum transfer.
You want a careful balance here. Too much energy in too small an animal will make things, let us say, much messier. All you want is a clean take.