Aperture horribly slow on Retina Macbook Pro 2.6/16/512

Aperture is terribly lagging on my RMBP despite maxed out CPU and RAM. I notice that only 1 core (2 threads) is utilized and at 100% all the time as I'm looking through photos. As I'm trying to move from picture to picture there is usually a ~ten second lag and the entire computer stalls as it tries to progress (meaning I can't even look at my email or a browser while it tries to go to the next picture. This is NOT while it is importing new pictures btw...it happens again and again long time after I have imported the pictures.

My questions are:

1) is this normal?

2) why is aperture not utilizing all 4 cores/8 threads?