hey no1stunna, I am no expert but this is what I think about our p5 racings...
Sometimes bodystyle does matter, but most of the time it's what's under the hood that does. Adding to the complicated equation are the factor or weight distribution, suspension and others I can't name all. Our P5 may look slow in terms of a station wagon form, but it's also by no means heavy. Mazda also did an excellent suspension job in this car. In comarision to the same class Matrix (heavier, less torque), VW Golf (2.0 115hp one), Civics (SOHC vs. our DOHC, less hp) is quite competitive.
In terms of bodystyle the F-150 Lightning has a supercharged V8 with almost 400hp, BMW M5 has 400hp stock, Mercedes ML55 AMG.... you name it, so I think that's more in a race-able car then it's look.
Also in your case the stunt bar you changed will probably changed the dynamic of the suspension setup, I can't be sure if yours is worst or better, but it doesn't really matter in terms of the fast or not issue, what matter in this case will be your conering characteristic. Again I can't be sure if it will get better or worst, but it definitely make somewhat of a different when you coner your P5 hard...
Oh oh oh, almost forgot, yes it is ok to race the wagon, in fact this is what I am planning to do, race my P5 hehehe.... you just have to know your limit when racing people. Don't bother revving your engine with a GTI or M3...