It doesn't matter if the card sticks out more than the mainboard does, as long as it can fit inside your computer's chassis. As for power consumption, does your power supply have that 6-pin PCI-e power connector natively, or are you using a converter and two regular white 4-pin molex connectors? If the latter, you might want to make sure that your PSU can deliver high enough amperage on the 12 volt rail for the card. If you don't know a lot about that stuff (I don't know what you know, so I'm just safing it :p), you could use your cell phone or something to take a picture of the label on your power supply, and upload that so we can see it.
It's likely to look something like this.
Different wattage PCI-e power connectors generally have different number of pins. You have some cards that require one 6-pin power connector, others that require one 8-pin, and even some that require two 6-pin or a 6-pin and an 8-pin connector :p
Sure, but if I get an nVidia, I don't have to deal with that craphole that is Catalyst and its control panel :p.
-edit-
Now that i think about it, I might have been the GTX 460, not the 465 I had been looking at. It's supposedly better and cheaper than the 465.