I have had both.. I used to drive a 400whp SRT-4 and now I drive a 04 Cobra. As stated previously, they are different classes of cars. The SRT-4 costs $21k and a 04' Cobra is $36k (sticker) - you can't compare the two.
I got rid of my 04' SRT-4 because of traction. I was tired of spinning in 1st, 2nd, and 3rd gear and going no where fast. Sure it was fast from a roll - but that is not real racing. It is not practical to drive on slicks all the time, so most of the time I would get my ass handed to me by cars with traction.
The 04' Cobra is a totally different beast. In stock form, from a stop it was WAY faster than my skittle. It has what I am looking for and can handle way more that the 550whp the stock skittle engine can (which is impressive for a 4cyl). I have seen the 03-04' Cobra engines do 800whp on stock internals - no problem. I see a Whipple in my future
The point is both cars are awesome. It is just a matter of personal preference and how much $$ you are willing to dish out to go fast. I dumped $12k into by skittle to get it to 400whp. I put $2k into my Cobra and it is now above 500whp.
Mustangs have always been in my blood. I have owned over 8 of them and I knew one day I would get back into them. You can't beat the bang for the buck.