Exactly the same behaviour I have seen. I actually gave all green to the win8 regarding WinSPMBT couple of weeks back. Now that I have the CD version and I know what to look for the lag is really there even in the 800x600. I also noticed that you can't alt+tab from the game and then go back, this will mess up the colors and the graphics to an unplayable state. Playing in windowed mode isn't that bad however. I can check the internet, chat with people etc. when playing which is quite nice for a turn based strategy.
Re: Windows 8 Playtesters required
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