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Macworld tests games at 1024x768. Not a resolution that is going to show off the capabilities of higher end video cards.

The difference will show up at higher resolutions like 1600x1200 or 1920x1200. Look at pcgaming benchmarks to get an idea of the difference between the 2 cards.
 
Of course they are almost similar, look at their names! I haven't look at the clockspeeds but I guess that GT130 is just GT120 with 512Mb of GDDR3.
 
as someone pointed out, they are being run at 1024x768 which does not exactly tax a video card, let alone show the advantages of having more memory dedicated to textures/etc.
 
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