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#11
If you are located where you can buy from Newegg, use their memory selector. The Asrock board that you've chosen is included. I suggest buying a dual-channel kit, for which there is no price premium.
The cheapest:
Newegg.com - G.SKILL NS 4GB (2 x 2GB) 240-Pin DDR3 SDRAM DDR3 1333 (PC3 10600) Desktop Memory Model F3-10600CL9D-4GBNS
cheap DDR3-1600 (will run at 133 unless you use an XMP profile):
Newegg.com - Crucial Ballistix sport 4GB (2 x 2GB) 240-Pin DDR3 SDRAM DDR3 1600 Desktop Memory Model BL2KIT25664BA160A
something from Corsair:
Newegg.com - CORSAIR 4GB (2 x 2GB) 240-Pin DDR3 SDRAM DDR3 1333 Desktop Memory Model CMV4GX3M2A1333C9
and the least expensive dual channel HyperX:
Newegg.com - Kingston HyperX Blu 4GB (2 x 2GB) 240-Pin DDR3 SDRAM DDR3 1333 Desktop Memory Model KHX1333C9D3B1K2/4G
As regards overclocking, it's hardly a normal thing to do. I tend to overclock as a matter of course, but the following considerations apply:
You may need a better heatsink/fan than stock ($$$).
An overclocked PC may be happier if the room is not warm.
The life of the CPU and other components may be shortened.
The stability of the PC may be reduced.
Your warranty may be affected.
As for using Win7 Enterprise, how do you intend to acquire it? (You probably shouldn't respond if it's to be pirated.) It's not available at retail. It's basically the same as Ultimate. I'm not sure what it lacks compared to Ultimate. (Language packs, probably.)