Kia is actually late to the party.
Mazda 6 GS - Most "sporty" of the Japanese 4?
Nissan Altima S - fairly "sporty" for what you can get in a $30k sedan w/270hp?
Honda Accord EX/EX-L
2012 Toyota Camry SE/XLE - apparently the SE is actually "sporty"
Hyundai Sonata (does it really count?)
I think what the Kia SX brings is the additional feature-content that most of the above compete with for $2k more.
1) I wouldn't necesarily put the Mazda 6 at the top of that list. It is certainly one of the sportier entries, but not as aporty as the zoom-zoom tag line would suggest.
2) I would not put the Accord on that list at all, unless you mean the Accord Coupe.
3) I would include the Sonata 2.0T Turbo. Doesn't handle quite as well as the Altima 3.5 (which is the car I owned before the Sonata), but isn't far off. It's also a lot closer to the Optima SX than some suggest. I had a quick turn behind the wheel of an Optima SX Turbo and the similarities with the Sonata 2.0T were by far greater than the differences - which is hardly suprising, given the common chassis, engine and transmission.
4) I would add the passat 2.0T to the list.
Jaeger