576 is what you get is if you estimate it at 24x24, 600 is what you get if you estimate it with a ruler based on the package size, and and 583 is the official number from NVIDIA. Happy now? In fact to be even more precise, NVIDIA claims it's a 24.3x24 chip...
I'll be happy if you keep those disrepancies in mind when estimating future dies *har har har*
And don't forget - GT300 is the real LRB competitor from NV so i wouldn't be very surprised if it'll have loads of programmable memory/cache on die - Larrabee style.
Well I personally doubt that LRB could shoot up to such magnitudes of die area as GT3x0 and even then power consumption might be higher for the first.