Perfection From Perfection

There are many concepts that Descartes talks about that I respect. However, I find fault with Descartes in Part Four when he attempts to explain the existence of God. Descartes, after proving the existence of the human soul, says that, "Following this, reflecting upon the fact that I doubted and that, as a consequence, my being was not utterly perfect, I decided to search for the source from which I had learned to think of something more perfect than I was; and I plainly knew that this had to be from some nature that was in fact more perfect" (61). I read this to mean that in Descartes' mind, perfection can only come from something that is, itself, perfect. Descartes sees this paramount perfection as being God, yet it seems that the idea of perfection from perfection is flawed. For example, I am imperfect in the sense that I can't run fast. Now I can imagine someone that can run faster than me, but that in no way means that they exist. All I did was heighten one of the traits I lacked. Another way of looking at this is that all one would have to do to reach this idea of God is to exemplify to the highest degree attributes already or partially held (wisdom, power, strength). These are human traits that already exist. This shows how we can arrive at the concept of God without any existential assurance. Essentially, we can arrive at the idea of God by thinking of a being that has our traits at the highest level. This does little in affirming his existence.