the infinity is better if you want a louder fan that moves more air, while the ninja is better if you want a slower moving fan that is quieter or no fan at all.
http://www.silentpcreview.com/article658-page1.html
"While both heatsinks are clearly excellent performers, a side by side comparison leaves no doubt that our Ninja sample is the better of the two ? at least with low airflow. The difference is not great, but it is there.
Nevertheless, we should stress that these results apply specifically to low airflow situations that are of interest to silencers. It seems quite likely that the Infinity could reverse the standings if the two were tested with a noisy, high speed fan, as it would be helped by its larger size and the closely spaced fins around the heatpipes."
oh and what do you need with more than 4 cd-roms? It always depends on what case/ cases you are referring to.. but that's a good generalization.