I heard bad things about the washer mod. Sounds like you should get the short tails.. one just sold yesterday for $250..
AAM Short Tail Exhaust - YouTube
Also, this is the comparison to another cheap exhuast setup.. gains +27hp and has a great sound..
Nissan 370Z Z34 09-11 Top Speed Pro-1 Catback Exhaust System Systems Resonators | eBay
Top Speed Pro 1 Performance - 370Z/G37 True Dual C - YouTube
P.S Is the 370 much better than 350? I was gunna get a 350 before i drove the 370z