Stock rockers are variable ratio. On a XP cam I measured roughly a 1.78 ratio at full lift. A 1.7 roller will lose some ratio at peak lift... I was not able to measure it accurately though.

The last motor I built with rollers used 1.8s, custom rocker bolts, custom lifters, and a xpz style cam on double spring 150# springs.... I still think it floated slightly passed 6400rpms so i shifted it at 6200 instead of the targeted 6600....