They're hard to find, but occasionally someone will dyno before/after just a ratio/rocker change. Two recent ones in Mustang-related magazines came up with the following results - and they are the biggest and smallest changes I've seen related to just a rocker change. One added 1.7's to a reasonably modified 5.0L normally aspirated. It had the 'usual' - heads, cam, intake, exhaust mods. Addition of the 1.7 rollers actually caused a loss of 1HP at peak. Throughout the range, there was basically no difference before and after - some points it was up by a HP, some points it was down by a HP. CarCraft recently built a carbed motor based on a stock block HO 5.0L with HO cam, AFR165 heads. Addition of 1.7's added 17HP to their set up - they attributed it to the fact that the head wanted all the additional lift it could get.
For your stock engine, if you're getting them inexpensively, they probably won't hurt anything and I'd install them. However, I wouldn't get to excited about potential gains. If you pick up 5HP at peak, I'd consider that a win - so be sure you're getting them cheap.
For your stock engine, if you're getting them inexpensively, they probably won't hurt anything and I'd install them. However, I wouldn't get to excited about potential gains. If you pick up 5HP at peak, I'd consider that a win - so be sure you're getting them cheap.