Slower Rendering in 4.5?

I recently upgraded to 4.5 after using 3.0 for a few years. I like the stability of 4.5, but have found that most of my files take much longer to render when rendering into Quicktime in 4.5

Even when I save the old 3.0 file as a 4.5 file (which subsequently cleans it up), it still takes much longer to render.

I’ve noticed it’s to the point where in one comparison, a file rendered in 3.0 would be completely rendered, where as the same file rendered in 4.5 would be sitting at less than 20% complete in the same time.

Is there anything I can do to speed up the rendering in 4.5?