The X-FI's sound fantastic, so much better than the on board audio, and you paired it with some good speakers. Add another gig of RAM and thats money well spent in my opinion.
Depends how far you are going to be honest. The performance stuff is more stable, but unless you o/c then it is pretty irrelevent. I could have probably lived without mine, buit at £58 a pop it was ridiculously good value.