Harland Sharps website claims that their "...unique Friction Free Design has shown average performance gains of 15 to 40 horsepower." Maybe so.
The higher number ratio opens the valves quicker and slightly farther making your stock cam act like a more performance oriented cam.
I believe in the 2000 engines that the factory ratios were already 1.6 so to go up you'd need 1.7's
Basically the fulcrum point gets moved closer to the push rod end of the rocker making the valve tip end of the rocker move quicker and farther than before.
It works to help any engine, not just supercharged engines. The needle bearings in the fulcrum also help some in saving wasted mechanical power and some manufacturers claim it lowers oil temperatures as well.
It also keeps your valve system more dimensionally consistent in it's operation from valve to valve allowing the engine to operate more like it was designed to. Add that to the fact that the rollers and fulcrum bearings don't rob as much power as standard rockers and it could add up to a significant number of horsepower gains.
Stock valve trains are the limiting factor in higher revving engines, due mainly to valve float from insufficient valve spring pressures and mechanical inefficiencies, and therefore roller rockers are almost always used, but your application won't likely have that problem.
Another thought from some is the roller lifters themselves will limit your rpm capabilities to around 6250 simply because they are so heavy. They add a lot of inertia to the up and down opening and closing of the valves making valve accuracy a tough thing to come by.
You can keep the same lifters and everything else if you like.
One thing you should check is whether or not your valve covers still work with the new rocker arm setup. The others on this list would know that answer.