In reply to Marek:
Yeah... that's where I run my 28 road tyres as well... front 70, rear 75. I'm a bit of a newb to gravel biking but was still surprised when I read the recommended pressure on the tyres (50 - 75 psi). I'd just plugged a hole in the same tyre as well, so I plumped for just above half of the recommended pressure to test out my handywork.
I think I'll play it safe and go for new tyres. Really liking the Goodyears recommended by Toby on the other thread... have also read some other reviews now and they seem to be highly recommended.