Question about PC's

[Kayla]

the i5-2500K is more than enough and easy overclock-able to a clock of ~4.0 GHz, which is more than enough for gaming. If you got time you wait till next year for the Ivy-Bridge getting released for the LGA1155 Socket (if you want / have this socket)
If you have to buy a Motherboard to the i5 don't go for the H61 socket, look for P67 or z68 or similar, since they're overclockable to higher values than the Intel Turbo.
Liquid cooling? You want an own loop or watercooling like the Corsair H100?
6 / 8 Core CPU's aren't even supported from the games, so it's senseless atm, except if you want to do stuff like Folding or BOINC in the background.
To the GPU: depends on your money available, the more money the better the GPU ofc.

PSU Wattage:
http://extreme.outervision.com/psucalculatorlite.jsp
use these settings:
Motherboard: High End Desktop
CPU TDP - 90%
System Load - 90%
Capacitor Aging - Leave blank as "Select"
This will show you a good result as recommended, go a bit higher than it ofc.