2002 Honda Accord SE

Hey i have a 2002 Honda Accord SE. I have the stock muffler and the stock catalytic converter. I was wondering in the stock cat was restricting my power/performance by alot. I was also wondering if getting a new muffler such as a universal magna flow muffler would improve power/performance by any amount. I dont want to buy a completely new exhaust system because i already have upgraded headers. If anyone could help answer these questions that would be greatly appreciated
Thanks,
Matt