I read it in a 5.0 M&SF awhile back they dyno tested mods individually (can't remember what issue it was on) but I'm almost positive they lost 1 or 2 hp. It's basically a mod that helps you out when you have other supporting parts in place already.
You can see a gain from 1.7RR's if your valve springs are in good working order. Reduced friction and a bit of increased lift. I was happy with mine. Don't expect nothing spectacular but you might feel the gain and you might not. Expect 5-8rwhp if the springs are up to par.
Its much easier to install rockers then a cam. Theyre actually simple bolt ons, the adjustments are the most difficult part. Upgrade the springs and you will feel a difference throughout the powerband. I did get valve float with the stock springs over 5000 rpms, so its a good idea to change them.