i am a goalkeeper by trade. Whilst certainly the art of saving a pen involves a lot of guesswork and luck, there is a technique and a certain set of attributes.
The stats that keepers like dudek/cassilas/reina (all top pen savers in real life) share are cenrtainly agility and reflexes. You are often guessing/anticipating which way the striker will go, this guess can be deduced from his body shape, which foot he uses, where hes looking
(theres plenty of other tell tale signs, keepers amke good poker players lol)
Combine this guess with top agility/reflexes and you have a much higher chance of saving a pen than a big, tall, bulky (not slow but certainly less agile) keeper like kirkland, cech etc. And thats not to say the likes of cech/kirkland wont save a pen, but im pretty confident casillas/reina/dudek have better penalty saving records.
i am aware im straying off topic like i warned others not to, the perk of being a mod eh?