here's some real information regarding the 03 adn 04 srt4s
03-05 srt4's all have the same power. the 03's were rated at less, but power is the same. injector size changed, but power didnt. they just ran larger injectors and cut down injector pulse
04-05 have LSD units. due to the equal length halfshafts accelaration is not hindered much between the 03's and the 04-05s. the LSD comes into play in accelaration out of the turns, it helps prevent smoking the inside tire coming out of the twisties
an 03 is going to be cheaper and will do just as well. when it comes down to the LSD, i dont like mine. i have an 03 with an 04/05 LSD. it causes too much understeer. stick with an 03 and save a couple bucks