My pihole currently lives on a dietpi install on an odroid c2 clocked in at 1500 odd mhz, over the last year it has been on several things like a pi zero, pi 3 and various other pi type sbc as i seem to have a lot of them.
The c2 its on at the moment is well overpowered, especially as i am using its emmc option which is faster than a flash card - pi hole harldy touches it when running and even hitting the gui or updating the thing its loading only a couple of cores pretty low.
Its attached to the back of my vodaphone hub via a usb cable which powers it and a lan cable, no wireless in use. It doesnt currently do my dhcp (left that to the router) but of course does do dns duties.
Its going to be running as an ip cam recorder for security soon as well, thats not going to use much grunt either - plenty to spare and its not even overclocked, although there is prob 10% there if need be.
Bit messy but hey its never touched. Just noticed it needs a system update, prob do that at the weekend.
Pihole is great, everyone should have a pihole setup - speeds up browsing and makes things more secure.