Stock Jetting is pretty good. I ran the PC pipe and Delta Reed valve with stock jets at sea level and temps from 40F to 85F all last summer with no problems. Ended up putting the stock pipe back on to get back low end power (left the stock jetting) Would like to try the FMF with the power valve shim. Wonder if anyone has ran both the PC pipe and FMF w/ shim and has a comparison?
I haven't had a chance to try the PC pipe, but I run an FMF Fatty and a VForce on my '03 KX and for me the FMF pipe is better than the stock pipe everywhere.
I was out riding with a guy a while back who had a PC on his KX('03 250), and, like you, he said that the PC had much better top-end than stock but lost bottom. He preferred it that way as he was coming off of a 125. I think you might like the Fatty better than the PC as long as you don't crave alot of top-end(the Fatty has better top than stock, but not a whole lot). Also, the PV spacer went along way toward filling the gap in the lower midrange.