1gig is more than enough, I have had the same issue over time but with other payware from IRIS ( fighter jets ), Carenado ( Small GA aircraft ), CLS ( MD80 and MD87 ) etc.. its not an aircraft/scenery bug but more of fsx bug with modern hardware that can happen from time to time :(

If you use an app like GPU-Z you can monitor the amount of gfx memory flight sim is using. On my pc it tends to use a max of 480meg but if i max out the AA quality i can force the sim to use almost all of the gfx memory i have.