We don't have any valve train upgrades for the 500 HP EFI. There's not too much left in it naturally aspirated. Az. Speed has a larger throttle body and different program that will help out a little bit, but you really need to work with the heads, replace the heads, etc. to get much more out of it. I've worked with Paul Pfaff on a NA setup that was similar, you might want to contact them.
Reckless, stage one is very easy to install, 3 connectors and 4 bolts to remove ECU, then filter and thermostat are a simple. This program is for 91 octane and will void the factory warranty, theres nothing we can do about that. There is a 2 day turnaround time, shipping depends on the area, weight and delivery time requested.
I do not put much faith into 15hp per mph, every boat is different, and V bottoms are the toughest, some boats will take more per mph, some less. I've seen boats with another 50+hp go the same speed. Certainly 15hp per mph is a rule of thumb, but like I said, everything is different.