EPS12V PSU and question about 12v rail mixing

First of all I wana say that my english isn't as good as I wish but I'll try.

I have Fortron FSP460 60PFN. It's rather old I think but served me well so far. The problem is that I wanna connect 9600GT video card but the PSU doesn't have pci-e power connectors. It has two 12V rails(fist one has 16.5A(CPU line) and the other 15A(I/O line)). I know that there are molex to pci-e cables but I have other idea here. The PSU has two 12V CPU power connectors. one 4 pin which is used at the moment. And one 8 pin(used mainly in server motherboards) which I don't use. I was thinking to use it instead of pci-e connector. From the pictures the only difference I noted is that pci-e connector is turned at 180 degrees(the 12V and GND cables are switched which shouldn't be a problem I think) and the extra 2 pins. Sorry for my bad english here but I can't explain it better. Can I connect it that way? Will there be any problems? The main reason I want to do that is because I want to load two 12V lines equally. Only the 4 and 8 pin 12V connectors use 16.5A's line. And everything else including the 24 pin power connector uses the second line. The thing I can't understand here and need help for is this: Where the pci-e X16 slot takes power from? The 4 pin connector or the 24 pin? The CPU is clear. But same question stays for me for memory, chipset and all the other componets on the mainboard? Can anyone help here? However I think that the CPU line is build to power 2 or more CPU's so it will be good to change the second one for video card. And now for the other question: Assuming that I connect the unused 8 pin connector instead of pci-e connector(takes power from the CPU line) and the power that comes from the pci-e x16 slot itself uses the other line(I/O). What will happen if I mix the lines that way? I hope I've explained well enaugh everything. I wanna as well ask which line takes the more load in my case:
CPU: E6750@default
MB: Gigabyte P35-DS3R
VC: Galaxy 9600GT
two HDDs
two DVD/CDs
two sticks DDRII memory
two additional PCI cards
Some fans as well and some usb devices

Thanks in advance.