if you have a smsp header i would suggest going with one of his exhausts as well. you dont want any bottlenecks if you want max performance.

my brother had option 4 on his gsr except he had an 18" resonator instead of the 22" along with a carsound cat and jdm itr 4-1 header. it was a little raspy while below vtec which could have been negated with the bigger resonator but above 4400 it screamed. a good scream.

as for the mugen muffler, might as well get a hytech. same twin loop design but in 2.5".