^ Dont believe that.
More memory doesn't increase performance considerably. Only increases it significantly, and I use that term lightly, if you are playing at a resolution much higher than 1980x1200 and/or if you have two monitors.
So if you play at 1980x1200 or anything below that, more than 1gb wont be necessary.
And to answer the question, if you play at 1980x1200, the 1GB at 950 MHz will suit you better, and if you have two monitors at that resolution, or a resolution thats higher, the 2GB will be better.