Its been several years since a build and it seems ive forgotten more than I thought.
I have the i3 540 and my motherboard has an 8 pin CPU power connector. Is it ok to use an 8 pin or should i just stick with a 4 pin?
Read your motherboard manual. Most of the time it will say that using only a 4 pin connector is OK unless the motherboard needs extra power for overclocking or for added pci power to handle a strong video card.
However in this case, you have an 8 pin lead for an 8 pin connector on the motherboard. That is exactly the intended use.
You can safely use either. The 8 Pin connection is required for Processor => 125 Watts, which you are well under. Is there an advantage to using the 8 pin connection when only a 4 pin connection is required - Yes. It reduces the I squared R losses at the connector and the wires / MB traces. Again, not a biggy in your case, but if you have it, use the 8 Pin connection.