[dathinab]

really quick still doesn't mean it's free, especially if you always have to zero all the allocated pages even if the process might just have used part of the page.

Also the question is what is this % in relation to?

Probably that freeing get up to 5% slower, which is reasonable given that before you often could use idle time to zero many of the pages or might not have zeroed some of the pages at all (as they where never reused).