I'm not overclocking but due to noise reasons I replaced the original Adda 40mm fan on my MSI G3Ti200 with a Papst 80mm fan with 7.5V mod. The temperature using MSI HW monitor went down to 39C from previous 49C and it doesn't make any noise anymore.
I just put in top of the original pretty big heatsink with 3M double-sided tape. Of course it takes two PCI slots but I'm not using them anyway. I'm happy with the setup. It's not pretty but it is quiet and cools well.