a few questions for you.
Are you going to build the PC yourself?
Why a Matx Board for $170 when your gonna put it in a mid tower (antec 900)?
Are you using the PC for Home Theater (since the p5q em has HDMI and opitcal) ?
Since your not worry about a mid tower chassis, i suggest you get the Asus P5Q-E for $176, an ATX mother board is a lot easier to work with and last lots of room for upgrade and better chipset cooling. Or you can take a look at the p5q pro for $140
Those OCZ Platinum XTC rams require quite high voltage for it to come alive, i personally own the OCZ platinum 800mhz 2gb.
With the P5Q EM you wont have enough system fan headers for the antec 900 fans. That means you be stuck with using antec tri-cool fans or you need to get one of those fan controllers
From my personal experience, P5Q series have a really easy overclock features

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