So, I am wondering what the distance of a .30-.30 is before the range drops off. considerably. I am looking to purchase a new one.

stuck, I don't push it more than 150yds. I always chamber a PSP for my
first round. I have a Win 94 carbine, Mar 336c and a Savage 24V 30-30/20ga.
I prefer the 336C over the 94 carbine. The Savage I use when the brush is
real thick.

With practice and a scope 200 yards.

I dropped a deer from about 225 with a 30-30 but I wouldn't recomend it unless you had a stable rest, knew the exact range, and had lots of practice. I held over about 12 inches and put a 170 grains right where it's supposed to go. She ran for about 30 yards before slowing to a walk, took about a dozen more steps before dropping. Flat pointed bullets expand very well even at relativly slow velocities and this one did too. I found it lodged in the meat of the ribs opposite of the side I hit her.
The damage wasn't spectacular but her chest was still filled with blood.

The 30-30 packs respectable numbers and results out to 200yards with both 150-170gr loads for deer size game. If your looking to hunt larger game such as Bear or Elk I would say 100-150yards would be your limit.

For a 30/30 I'd try to keep my shots inside of 150yds. However, 200yds. is not out of the realm of possibility if you have a good, accurate rifle, scoped, and have practiced with it at the longer distances.
Rifle suggestion: Marlin 336 with Weaver 1-3x scope.
Ammo: stick with the 170gr. bullets.

zeroed 3inches high at 100 yds and you can shoot point blank to 200 for deer.(bigger game should be within 125-150 yds or closer) Nothing further than that as energy and trajectory really take a nosedive. check out a trajectory/ballistic table.

stuckinthereeds,
The 30-30 is a great short range deer cartridge and will do the job out to 200 yds with practice. I limit myelf to about 150 max.

stuckinthereeds,
I might also add, I self limit myself with a 30-30 by using iron or peep sights only on my 30-30's. This helps keep me from "pushing the envelope" on range.

I have always kept my .30-30 range at 200yds or less.
I have a Marlin .30-30 that was given to me by my Dad when I was 12. It will always be my favorite gun.