Of the two given rounds, I would go for the 7mm rem mag for a number of reasons.

1. You are already familiar with a shotgun's recoil, which will be less in the 7mag.

2. The 7mag is a very significant step up. With 150gr powerpoints, it will darn near rip a deer's shoulder clean off (if hit there obvouisly)when you go to process it. My point being: if you need for a deer to fall down straight in it's tracks to avoid a creek or a fence, it is fully capable of the job. If that's overkill to you, then there are plenty of tougher bullets on the market including just stepping up to the 175gr powerpoints which are pretty easy to find.
And if you ever wanted to go out hunting for some of the larger animals like elk, you are going to want the 7mag over a 7-08.

3.Remington makes Managed Recoil ammo for the 7mag, which means you essentially have a 7-08 if you want it.

I'd just keep shooting the slugs though :cool15:

7mm-08 all the way.. IMO it is about the perfect deer round

As you may know the "caliber" of these two is identical - 7 mm. diameter bullet. Obviously the difference is in the powder charge behind the bullet !!! The 7 mm Rem. Mag. is considered a "long action" round and the 7mm/08 Rem. is considered a short action. The 7mm/08 Rem. is derived from the 308 Win. case, necked down to 7mm. It is a superb deer round which has a relatively easy to manage recoil. This cartridge does great with 130 gr. bullets. As a shotgunner, however, the 7mm. Rem. Mag. recoil should present no problem at all. The 7mm. Rem. Mag. and 150 gr. bullets is a super choice for medium game. For my hunting area where shots are seldom over 150 yards .... and how I hunt (tree stand or ground blind) ... a 7mm./08 Rem. in a top quality , 20" - 22" barrel rifle would be my choice.

Get a smaller caliber. The 7 mag is twice what you need for deer. If ya go that big get the 30-06 but that is even way upper end for deer. 7-08 is nice, 25-06 is all ya need fro wis.