Thanks for the replies, looks like OAG is the way.
Few things, the G4 16000 has its own OAG and I think it’s the only OAG that will fit it.
Without spending even more money I will be using my 174mm as it has a larger FOV. I’ll be aim to do 10 second guide subs, so that could be enough time to pick up faint stars. I can even bin it.
https://www.gxccd.com/art?id=436&lang=409