In my experience with Rodinal 1:50 to 1:100 with various films, it usually results in 1/3 to a full stop less real speed than the ISO rating. That's why it may not be good for pushing; there's not much point in losing up to a stop in shadow density before you even get started.(posted 8715 days ago)PQ developers (Microphen etc) usually give up to 2/3 stop _increase_ in real speed for a normal CI...so it's as if you're getting something for nothing. Then you push (simply increasing contrast) from there.
So...based on the same CI...HP5+ in Microphen 1:1 or DD-X 1:9 gives a _full stop_ more real speed than in Rodinal w/sodium sulfite, or iow, EI 640 rather than EI 320. As you can see, if all you want is EI 800 you don't need to push much.