Krunch,
If you install the GV stack per the RT instructions, it will most likely result in the mid-speed harshness I described. Several of us KDxers fought through that issue together a couple of years ago. I could do some digging, and see if I can find the stack I ended up with.
FRP might use something different today, buy my FRP stack in 99, was exactly per the instruction sheet. Hmmm... Maybe, somewhere along the line, I posted my stack on this board. :D
Comparison RT to stock. The RT will be head and shoulders above the stock system with the RT stacks. The bike will dive much-much less in the corners, yet gobble up bumps. However, as I stated, with the RT stacks, it's going to be a little sharp on some roots and rocks, and hammer you in those braking-roller whoops. Compared to MXT, I do not know. I've never ridden a MXT KDX. I can say this- the RM forks are much better than RT KDX forks.
The RT video is worthless for working on the KDX forks. As mentioned, it covers KYB and Showa, so it is a good reference video for some other day if you switch bikes.
But, to the good news, is that KDX forks are waaaay easy to work on. If you go to the Just KDX section, you'll see the fork tool I drew up. With that tool, a person of average mechanical ability can easily install the GV kit. Owning the KDX shop manual is also EXTREMELY helpful. Once you have it figured out, you can change the valving in 1/2 hour by pulling only the base valve out the bottom. (lay bike on side or all the oil will run out.)
Take note of this- After you get the front end sorted out, you're going to find that the shock needs some help REALLY bad. It will kick like a mean mule in the whoop sections, in which you can now rip with confidence, thanks to the improved fork. Unless Kawi has changed the shock valving, (and I doubt it since my 95 and 99 KDX were exactly the same,) there is far too much high speed valving. A friendly revalve will clear that mean streak, though. Note that I also had FRP valve the shock, but it was still too stiff and kicked in the whoops. I worked thru some valving changes and came up with a pretty good working stack.
Now the fly in the ointment. Once you have both suspensions up to stuff, the wheels and spokes will emerge as the weak links. Be ready to get the wallet open again. :(
Good luck with it! :)