hey guys I have a question I know that putting new headers on my 01 mustang GT will give me a good increase in HP but I am kind of confused with them.

See I bought a BBK off road X- pipe ( which is on back order so that sucks but ) and I was going to get some flowmasters to add to it but I wanted to finish the system with a nice set of headers but here is what I don't get.

They have headers that are short and some that are long whats the diff? What do you get better than the other one? And what does that mean for my X pipe if I get long tubes? does that mean I will have to cut the X pipe to make the long tubes fit?

If anyone has any help they can give it would help me alot and if you all know any brands that are good thats has given you all good HP gains and sound let me know that also.

Thanks