I NEED HELP!! i' m thinking about switching to alums b/c you can tune alum arrows to shoot bh' s better, or is that wrong?... how much will this slow my arrow down??? will i still be able to use a pendulum site and it be accurate? what is a pendulum that is adjustable.. i' m using a Hoyt Vortec bow.. not redline or versa cam, the other one.. 27 in draw and 70 lbs draw weight.. someone HElP... please..

As far as accuracy goes, I don' t think one type of arrow is more accurate than another. Some may disagree, but I' m pretty sure most arrows made today have the potential to be more accurate than most archers shooting them.
Will aluminims slow you down? It depends mostly of the weight of the arrow, not of what its made of. A heavy carbon can be slower than a light aluminum.
Can you use a pendulum with a slower aluminum arrow? Most definetly yes. My old set up used a 2315 flying at 235 fps and my savage pendulum was good out to 30 yards from 10-25 foot up the tree. I never tried to shoot past 30.
An adjustable pendulum? All are adjustable as far as sighting in goes. You might be refering to the new savage that has a slide scale with yardage adjustment along with the pendulum.