I don't believe that you will gain 5-7 mph. I have used a loader in a 21 ft Eliminator closed bow running about 550hp. Currently have one on my Rogers running about 750hp and it does make a difference. Tried one on my 21ft Cobra and it made ZERO difference. Big heavy boat. I think the lighter the boat the bigger the difference you will notice. I also like that it pulls the jet down keeping you hooked up. Make sure you get the one that is rated for your application. Also $200 is high. I've seen several for $150.

When you install a loader, it's not a case of "bolt it in and you're done", especially if you are buying an "off the shelf" , "one size fits all" loader. You also need to see where the leading edge of the loader is relative to the keel. In most cases they will hang down well below.  You really need to trim the ramps back to get the desired balance between better loading of the pump and , for lack of a better term, "drag"
from the ramps.

Ray, your case is a prime example. The 500 rpm drop indicates that your pump is not loading very well without that loader. However, the fact that the boat feels like the tail is stuck to the water indicates the ramps hang too low. You should have cut them back a little at a time to find the proper balance. I have no doubt you would be gaining speed with a little trimming.

For the record, here's my story. Eliminator Sprint with a delta pad to which the previous owner added a small "bubble" ahead of the intake. Pump has been machined for shoe and rideplate and has a diverter.
Ran a pretty consistent 80mph at 5400rpm with a rock grate. Borrowed a friends loader and and saw a gain to 85 mph. Purchased a custom loader from Jack at MPD. At the same time, I acquired an Edelbrock QuickData and set it up to measure upper and lower intake pressures. With the loader installed "as-is", I saw 82 mph. Negligable rpm change. Upper pressures were way higher than the lower. Clamped the loader in a mill and moved the leading edge back 5/8"(which only raised it about 1/8"-3/16") and beveled the edge same as it had been originally. Again, saw 82. Rpm dropped about 50, pressures didn't change much. Took another cut on the ramps. This time I left the trailing edge of the bevel just in front of the access hole for rear mounting bolts, probably about another 5/8" shorter ramp. This raised the leading edge about 1/4". This cut took my speed to a consistently repeatable 89+ mph. Rpm was now 5200-5250. Upper pressure was still higher than lower but the lower was coming up compared to earlier tests. With a little time spent on ride plate angle and diverter angle, got it to 90.4mph (90.6 with header water off and Basset header mufflers removed). Loader has been cut back again and ready for another test but boat has not been back in the water. So to summarize, switching from a rock grate to a loader gained me 2mph. Trimming the loader ramps gained me another 7 for a total gain of 9mph. I have no doubt that the additional untested cut will bring a little more speed.

Your data is awesome...Now you know why we always build two loaders.....Cut too far, you can't get the sh!t back in the horse...

GT