06' 3.6 CTS - Mods

Bought a 3.6 CTS last week with 20k on it.  It is a base model but I am enjoying the car thus far.  I am wondering what mods to do to this car that will show decent HP gains.  The Volant or K&N intakes claim about +14HP, any idea what gains the Borla or Corsa exhaust systems claim.  The website state the flow increase but no DYNO testing that I can see.  Also...are there any good computer mods for this car?  If so, which ones?

Thanks in advance.

- Joel