"Things I know:
1. A typical motherboard these days, comes with a 24 pin bank for the power supply.
2. For some reason the average power supply these days comes with only 20 pins.
3. I can hook a 20-pin into a 24-pin board in most cases and be fine. Exceptions to this are:
a) Using a PCI-e vid card because it draws it's power from the remaining four pins
b) Using a board like mine that has a built in sound blaster card, which also draws power from these 4 pins
c) Using SLI "
I wouldn't say #1 is true. There are far more mobos for sale with 20 pin banks than 24 pin. 24 pin (ATX 2.0) is relatively new. Now if you're just looking at NForce4 boards, then yes, #1 is true.
For #2, see my comment above.
#3a is not necessarily true. I just built a system this weekend using an Antec 350W PSU (20 pin), a Chaintech VNF4 Ultra (24 pin bank) and a Leadtek Geforce 6600 VC (PCI-E). I'm also running a 160 GB Seagate SATA and a Benq 1620 dvd. No power problems, whatsoever.
I'm not OCing yet, but I plan to do some slight OCing like you.
From what I've read, a good quality PSU can go a long way. However, I've also heard that running SLI can really suck the juice.