From comparing them on newegg, the P5Q-E can support 16gb of ram and the Pro only 8, P5Q-E has 3 PCI-E slots (16x,8x,4x) and the Pro only 2 (16x,8x) although the Pro has 1 more PCI-E 1x slot that the E. They have different onboard audio devices (possibly, E is listed as ADI and Pro as Realtek, but the model # look similar so both might be Realtek), and the E has dual gigabit lan. There are a few other differences over all, but those are the most important IMPO.
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