I have a '97 KDX220 and my brother has '05 KDX220. I have the Pro Circuit pipe and my brother has the FMF pipe Gnarly pipe.
My 220 with the PC pipe still has a ton of low end. You wont lose anything on the bottom, but will have nice gains in the top end. I had a Pro Circuit silencer on it, but it did not have a spark arrestor, so I put my stock silencer back on and did not notice any differences at all.
My brothers 220 with the Gnarly does not have the top end mine does, but I also have the RB carb and head mod as well which makes a huge difference.
Hope this helps