I definitely don't know as much about exhausts for these cars. I do know ARK worked very hard with their 370z exhausts and were one of the top companies that people bought... I do know that their first version CBE did not produce as much power as a few others. They came out with another version later, but i'm not sure of the numbers on that... it was coming out after I sold my 370 and I haven't been back on the site in a long time.
I wouldn't look for them if you want the max power per $ though.