Is there much difference in these two products??
Would a lab suffer at all by going with the ultra puppy vs the ultra large breed puppy??
A large breed dog will expand in mass much quicker than a smaller dog and may need more protein and carbs than formulas designed for small dogs. Most likely in the large puppy formulas there is more protein and less filler (wheat/corn) in the feed. The cheaper the food, the more filler they tend to add... Your dog will be fine with either food as long as it doesn't upset the stomach. For smaller active puppies, 3 cups a day is recommended. Shannon and I feed Allie Purina One Large Breed Forumla, you will find many people feed many different things. I think one of the biggest differences for the large breed formula is they actually provide large bags so you don't have to get food every week. Might want to think about that, the large bag keeps us supplied for a month.
What I would personally do is take your current label off your dog food and compare it to the large breed stuff and make a judgement call based on the facts at hand. Once you make your decision, start figuring out where its the cheapest every week...