I am willing to build an E8400 + HD4890 rig, but can't choose which mobo (should allow to oc) to get. Also would like to know what ram is better for this setup and what how powerful psu should suit me. Thanks in advance
MB/PSU: GA-EP45-UD3P and Corsair 750TX if you want the option to add a second video card later. GA-EP45-UD3R and Corsair 650TX if you are sure one card is enough.
It really depends on your monitor. For 1680x1050 or less one HD 4890 is plenty, IMO. For 1920x1080 or more you should keep the Crossfire option.
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I'd look at the AM3 boards as well, it gives you more of an upgrade path as opposed to the LGA775 intel chips. The AMD Phenom II's are a great value and perform extremely well.