Have you ridden a 200exc? I just rode an '03 at DW and that thing was plenty fast for me stock. I would think for your stated use (assuming some tightness to the woods) that would be a much lower cost option. The SX design point is the lightest, fastest MX bike, so it's got 19" rear wheel, stiffer suspension, no lighting coil, etc. It's also going to be more of a top end bike, trading off low end where necessary. Porting and 39mm carb (vs. 38mm) is definitely different on the SX and is set up for moto, which again would point me to an E/XC. Pipe and such can change that some but only to a point.
Again, not sure about '04, but typically the SX's have the single piston ring design vs. the double rings in the E/XCs, meaning more frequent top end jobs. My local KTM dealer tells me the '04 200SX is a one ring but he wasn't totally sure.