We have had this debate for eons, with newer people saying its the amount of prims you wear..... the fact is, it is the alpha texturing that will make the ARC higher. As an experiment within a combat sim that I am involved in (as ARC levels were the major argument of the combat users), we showed, that with one change of hair, with less alpha textures in it, was enough to bring an ARC down from 5600 to 831.... that was a huge reduction. An alpha textured, prim item of clothing was then worn and the rendering cost jumped back to 2100. Yet we replaced the texture on the prim item worn to a non alpha, cloth texture and the ARC went down again to 831.
It's just that some people don't realize the major causes of lag, especially for script enabled combat sims, is extra scripts. Most of the time, resize scripts are a major contributor, especially in prim belts, and jewelry, where the prim totals have a script in each prim, sometimes this can total over 200 individual scripts.... a good reason to resize and then delete the scripts.