I have a 2006 trx 450 with hrc kit. The stock suspension has worked ok but the rear end is quiet bouncy.

BB485 said:

Yes it is worth every dime. I have it on my 400ex and I don't know how I rode and raced without it. It smooths out whoops, dips and ruts like you would'nt believe.

That is my next mod!

I am going to do the double springs, re-valve, extended travel up front and the rear with the link.

Have you done much adjustment with the rebound settings?  I would take out a little if it keeps trying to buck you off.

It sounds like your spring is a touch tight. Also increase the rebound resistance. Do these at different times so you can feel what the difference is. Your compression might be tight too. Does it buck as your hitting a bump or after?

I have an '06 with GT link and GT revalve. It works great, I have no complaints about it at all. super plush and forgiving if you case a jump or flat land.
My buddie has an '07 with all stock suspension. he has holeshot 20" front and 18" rear. I have to say that the tires make enough difference that if I had rode a stock bike with 18 inch rear tires i would not have spent the extra 180 dollars. I have riddin both at the track and have to say the stock tires are the biggest problem with the honda. I dont know what honda was thinking with the tire choice, but the single best mod to make to a 450R is TIRES.

How was their turnaround time?I'm thinking about doing this during or after I get my engine work done.

I would go with a ARS-FX or Derisi Racing set up

A suspension upgrade to include new springs and revalving to match your riding skill level and the terrain you ride is the single most important modification you can make to your quad, whether you ride recreationally or in sanctioned events.  More horsepower is not going to get you through the whoops or corners any quicker.