Nvidia cards system (hardware and software) card archatecture (sp?) designs just seem to work better with old games (which IL-2 most certainly is), unless those games were specfically designed to run with ATI, Radeon or other rival cards designs. Not meaning Nvidia are the best, just more devloped/stable or of a more broad ranged platform. (I am mostly quite wrong, but I always though the ATI was the 'US Made' gfx card for those who only buy 'made in my home country', where as Nvidea were for everyone else and Radeon were the Oriental market one that ATI borrowed/based lesser versions from)
As to what makes that plane a bit different, it could be to do with the 'materials' shading type used in-conjunction with some of the values in the conf.ini for various gfx settings...
Or have you tried at a reduced resolution or/and with differing anti alaising values. Or maybe its close to the poly limits - and theres so many graphical process per second happening that the card is just about keeping up with requirements? - might also see what video quality settings you have if they affect it...