I just replaced a 300w Antec PSU with the 450w AX450-PN. I can't tell any noise difference.
MBM shows the +12v running at 11.67v - 11.73v on my P4S533 mobo with:
P4/1.8 running at 2.4 GHz
2x 512Mb ram
1 HD
1 FD
2x CDRW
eVGA6600GT
lots of firewire and USB ports
external HD (firewire)
XP/home.sp2
I didn't check the Antec's 12v line with MBM before I replaced it. So I don't know how it compares to the Fortron. I'm a bit disappointed that the 12v line is running low. Yes, I hooked up the 2x2 12v connection. The P4S533 has a 20pin power connector, not 24 pin.