for what it's worth,I'm running a PC on my 2000 KX250,and I've always used PC on my 250s for years for their awesome mid to top performance...but after riding a 500 as my primary bike for a couple years, I wish I had gone with the FMF Gnarly instead for the low to mid(not that it'll ever have the low end a 500 has).
As much as I like PC in general...it's a mid to top pipe,and just doesn't have the low end snap I was looking for.
Hope this helps.