使用NSMutableDictionary与NSMutableArray>产生的性能损失

I am considering using an NSMutableDictionary in place of my current NSMutableArray. This is primarily for KVC/KVO reasons. The collection will undergo heavy mutation within the inner loop of my drawing method. Can I expect to incur a significant performance hit if I go ahead with this replacement?I am considering using an NSMutableDictionary i