I've been running some tests and have found that Quantum doesn't use significantly less memory as Chrome on normal sites, but does save the reported 30% on heavy, demanding sites. HF is one of those heavy, demanding sites, though.
I tested a particularly demanding page, one of those in the "What are you listening to?" thread in the Entertainment forum, which is chock full of embedded YouTube videos, and I also have HF set to display 50 posts per page. Here are the results from having only that one tab open:
Chrome + AdBlock Plus: 1.2GB (w/o JavaScript: 880MB)
Chrome + uBlock Origin: 700MB (w/o JavaScript: 490MB)
Chrome + no ad blocker: 500MB (w/o JavaScript: 380MB)
Quantum + AdBlock Plus: 800MB (w/o JavaScript: 720MB)
Quantum + uBlock Origin: 490MB (w/o JavaScript: 420MB)
Quantum + no ad blocker: 380MB (w/o JavaScript: 300MB)
Keep in mind that this is a worst case scenario: a very resource-intensive page on a very resource-intensive site (that's even worse in Chrome if JavaScript is enabled on the site).
As you can see, Quantum does deliver ~30% savings. What really blew me away, though, is what an obscene memory hog AdBlock Plus is, regardless of browser. I also tried plain AdBlock and the results were similar. I then tried uBlock Origin, an ad blocker that I'd never used before, but which advertises itself as being easy on the CPU and memory, and you can see the huge difference that it makes: ~70% less memory than AdBlock Plus. Naturally, most sites won't see 300-500MB savings, since they're far lighter on memory than HF is, but ~70% still adds up on lighter sites.
The main takeaway should be... whether you're using Chrome or Quantum, if you're using AdBlock or AdBlock Plus, switch to uBlock Origin now!
The lesser takeaway is that switching from Chrome to Quantum could save you a little bit more memory, but mainly on heavy, demanding sites, including HF. The difference on more normal sites isn't as much to write home about (look at how the results are closer with JavaScript disabled, for example).