I've been working on speed cards for a while now, though I had a pause for a while because I received LOTS of school assignments. But anyways, I've improved in so many ways!
Firstly, I've been practising my PAO-system a lot by trying to see my images as fast as possible. Works like a charm!
Secondly, I've been doing this thing that Jonas von Essen told me about; Grabbing 18 cards and memorize them really, really fast. That way you practise both your PAO-system, and your speed of your memorization. It's really effective and have improved my time by horse lengths.