did you overclock your processor?
i have the same one but it shows 2.0 GHz, also about the logic board, you said that its nVidia MCP75L where mine is nVidia MCP79 which is used in older macbook`s and its 100% compatible, maybe thats causing the errors you have? i think that not every K50 has the same board :|

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MSI P5Q / C2D E8400 @ 3.0 Ghz / 8GB DDR2 800Mhz / PCIe ECS 9600GT 1Gb / ALC1200 / Windows 7 / OS X 10.8
ASUS K50IN (SX004L) / C2D T6400 @ 2.0 Ghz / 4GB DDR2 800Mhz / nVidia G102M 512Mb / 15.6" HD/LED / ALC662 / Dell 1490 802.11g / Windows 7 / OS X 10.8