"Normal" Flag?
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Polymorphism
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Honestly, if speed is your issue I think you could only go so far with using arrays vs lists. Getting a fast update speed would be only half the battle I would imagine. When it comes time to actually draw the beast, you'll hit a wall on performance sooner than you think if you keep to blitzmax's standard draw commands (TImages with DrawImage and the like). Someone on these forums is making some sort of particle editor for blitzmax (made in blitzmax also?) that may have addressed the rendering issue of tons of sprites. I think in the end you may have to do your own calls to DX or OpenGL (I believe it's referred to as 'batching'). I think the name of the app was 'Splash' or something similar? Contacting him might provide some insight on speeding up particle simulations.
*EDIT*
was called splash:
http://www.blitzmax.com/Community/posts.php?topic=75201