[Buying Help] Internal Fan for SN45G

My SN45G is as follows:
Athlon XP 2500+ Barton
2x 512MB Corsair Twin-X PC3200LL
ATI Radeon 9700 Pro 128MB
2x 200GB Western Digital SE HDD
Lite-On 48x/24x/46/x16x CD-RW/DVD-ROM

I'm looking to cut my fan grill out and replace my internal case fan. I'm hoping to keep CFM near the same while lowering noise as much as I can. Right now I'm running my Sunon @ 5% with SpeedFan and the cooling is superb (40C). I just want to quiet this fan.

Fan options are as follows:

Thermaltake Smart Case Fan II
Fan Dimension:    80x80x25 mm
Max. Air Flow: 20.55 CFM at 1300 RPM & 75.7 CFM at 4800 RPM
Rated Voltage:    12VDC
Noise:    17 dB at 1300 RPM & 48 dB at 4800 RPM
Bearing Type:    Two Ball Bearing

Zalman ZF-1
Dimensions: 80mm x 80mm x 25mm

Specifications (resistor disconnected):
Airflow: 39CFM
Rotation Speed: 3000 RPM
Noise Level: 34.4dBA

Specifications (with resistor connected):
Airflow: 20.6CFM
Rotation Speed: 1700RPM
Noise Level: 20.0dBA

Vantec Stealth
Dimensions: 80x80x25mm
Airflow: 27 CFM
Noise Output: 21dBA
Rotation Speed: 2050RPM
Bearing: Dual Ball

Panaflo Axial
Fan Dimensions: 80x80x25.5(mm)
Bearing Type: Hydro Wave
Nominal Speed(RPM): 1900
Max Air Flow

CFM): 24.0
Noise(dBA): 21.0

So among the options above any any others you guys can find/think of, what is my best bet? I'm of the persuasion that dB doesn't mean anything in some cases as testing methods are not unified. So what do you guys think'll be the best solution?

My main goal is to have a silent system so whichever is the quitest while maintaing cooling power is the best option

Thank you all for your help and I'm sure you'l be seeing a similar watercooling thread coming shortly as I have questions about that

-bryce