Is this a good promotion?

Hi everyone!

Tl;Dr I have an opportunity to accept a management role at a different location w/in the same company, but that location is tiny compared to where I am now.

I'm a senior purchasing agent for a rapidly growing manufacturing company (I can't give the business sector, because anyone in this sector would know exactly the company). I've been with my current company for 16 years, and work under an absolutely brilliant supply chain expert. Our business was acquired a little over a year ago, and the new owners are really great. We've been growing rapidly, and have just acquired our 9th facility.

The location I'm in is the largest of the 9 by far (roughly $60m / year) and I'm the most senior buyer. Most would agree that I'm the heir apparent for the Materials Manager position once my mentor retires. The problem is that my mentor isn't very old, and probably has 15 years or so left to work.

The most recent acquisition is much, much smaller than us, at only around $1.5m / year. Their owner did all of the buying for the facility, and will be retiring in a few months after the transition to the new owners is complete. I've been offered the Materials Manager position for that facility. Taking the position would only be a modest pay bump because of the differences in the size of the facility.

On the one hand, it would be a title change to a management title. I would have a different bonus structure, profit sharing, etc...

On the other hand, the internal "prestige" would be a big hit. Being the senior buyer where I am is a significant position w/in the company, but being a manager in the other facility wouldn't be. For reference, I'm personally responsible for $8-10m in outside spend right now, but would be moving to a position where the total outside spend for the company is around $300k.

Any ideas? Is it better to be 2nd in command at a large company, or management at a smaller one?