adding a gpu block probably won't have much of an effect, if any at all. adding a block to the nb will again, have very little effect, if any. unless your looking to spend money, or want uniformity, there just isn't a performance reasons i can see water cooling them, given your current setup.
bix extreme II is going to be your better option. heater cores are more effective and have less resistance compared to radiators (bix extremes are nothing more than a heater core slightly modified to fit within the constraints of a tower). for $20-$50 (depending on size) you can get heater cores that may not be as pretty as a bix, but are easier on the pocket.
http://www.airspirit.net/ has a heater core database that can help you find a heater core to fit your needs, if the database is every brought back up.