Friction loss on stock 440 rocker gear

I've been watching the Engine Power tv series where they have been doing step by step mods to motors from various manufacturers. On a LQ4 GM and a 351 Ford, the first change they made to relatively stock motors was using roller rocker arms and roller tips on the valves. In both cases the gain was 15-20 HP. Any thoughts on what the improvement might be replacing the stock rocker gear with rollers on a non HP 440, say the early 70's mid compression motor? Seems like a good gain for very little work and a fair cost.
Tim

Actually depending on the kit, they can be a real pain to set up a set properly. If the rest of the motor is stock,I wouldn't bother.Good ones aren't cheap either. There are cheaper gains to be made elsewhere if you haven't already done so. IMO

The main reason for roller rockers isn't necessarily to reduce friction. It is for reducing wear on the rockers caused by high valve spring pressure. I can't imagine that roller rockers alone would account for 20HP. Sounds like a little fudging going on there.
Jus' sayin'.....

The only reason I could see for increased power would be correct geometry or more likely increased ratio. You'll find that there are lots of "experts" that write articles and play on the dyno. Some are Experts, some aren't. Take everything you hear or read with a grain of salt. Then make your own decision. With time and experience your decisions will make power and live.
Doug