Newegg is currently offering the best deal on Windows 8 Pro Upgrade copies, by offering a $40 mail-in rebate via prepaid debit card. This undercuts Microsoft’s own subsidies on the operating system and may be a sign that the software giant is allowing even deeper discounts in the wake of the slow uptake of the latest version of Windows compared to Windows 7 following generally poor reviews. The mail-in rebate offer with purchase is good until Sunday the 16th and the rebate form must be postmarked before January 15th in order to qualify.