Can't drive long NeoPixel strips with Due or Duemilanove?
Your Duemilanove only has 1k of RAM. That's not much. Each pixel takes 3 bytes of RAM (R/G/B). So (say) 60 pixels would be 180 bytes. That's less than 1k, but there would be other uses of RAM in your sketch. 

750 LEDs sounds like pushing it for the low-RAM Arduinos.

You might want to look at NeoPixels Revealed: How to (not need to) generate precisely timed signals The author managed to drive over 1000 NeoPixels with a Duemilanove.

I'm not sure if that applies to your exact type of NeoPixels, but it is worth considering.