Nope. You can't compare 5V fans with 12V fans or any others at different rated voltage. There are 5V fans that spin as fast as 12V fans or not, it simply depends on the specs. The rated voltage is not an absolut value but relative to the fan specs.
Now, the original fan is from AAVID, model 1447122 that is obsolete and discontinued. I can't find datasheet anymore, but from a site I found the following specs, but I don't know if they are accurate:
Volts: 5VDC. <-
ok
Amps: 0.13A. <-
ok
Speed: 6000 RPM.
?
Noise: 25dBaAir. Flow: 4.8 CFM.
?
Dimensions: 40mm x 40mm x 7mm. <-
ok
The Scythe fan specs are:
12V
0.06A
3500RPM
14dBa
4.11 CFM
40x40x10mm
So it spins slower and quieter, CFM is smaller but not a huge difference if you ask me, since it is also higher than the AAVID.
IMHO it is a fine replacement but if are not sure you must go for something else.