Top off water "limit"

Hi guys, I’ve been all grain brewing for the past two years, but having started grad school, I have less and less time to brew.
I’m planning an extract session, where I’d like to brew two batches out of the same wort.
I have an 8 gallon brewpot, and wanted to brew high gravity wort, split into 2, and top off.

What is the “limit” on topping off? Is two gallons too much? Will I notice the beer quality difference after 1 gallon?

Let me know what you guys think.

Before I started brewing all grain I used to top off my extract batches with 2-3 gallons of water(5-6 gallon batches). The beer was good, not nearly as good as what I make now but that is due to many factors. I don’t think you’ll have any issues with what you’re planning, might not be your best batches but you should be able to make some pretty good beer still.

I have about the same size kettle and I’ve brewed a few 10 gal batches, ending up with 6.5 gal in the kettle and diluting to 10.5. At that level I don’t think there are any real drawbacks to a concentrated boil, at least not for an average-gravity beer.

You should be alright. Many commercial breweries do a high gravity boil and then dilute to help get the beer out quicker.