I've done a lot of testing in this area but I don't have any exact wisdom to share. You can easily get 1.70 rockers if that is what you want. T&D sells them and so does Harland. If you are willing to machine your heads then you can get Jesel rockers in ratios up to at least 1.85 which is what I have on my Indy EZ heads.

The real question is what are you trying to do and do you need more rocker arm ratio in order to achieve that. When NASCAR engine builders were told they had to use flat tappet cams then they figured out that a ton of rocker arm was the solution to their need for lots of velocity at the valve. That doesn't mean that the average bracket motor needs either a bunch of lift or a bunch of valve velocity.

If you wander thru the Super Stock pits at any NHRA race and talk to engine builders you'll find out that a lot of them use rocker ratio to solve the problem but not always.

If you haven't read my article in Car Craft go find it and read it. I spent a bunch of time and money testing different rocker arm ratios on my 470 low deck. Zero power increase. We don't know why exactly but I suspect it is because the heads are already close to sonic choke so the extra valve velocity and lift were wasted. I could figure it out with more testing but even I have limits on the amount of time and money I'll spend on a project!