Very interesting insight ttxpetillo. I often render straight to PNG or JPG and I've also rendered to .EXR many times and I can't say I've noticed a significant difference. Maybe a few seconds for PNG compression, but it's certainly not a minute or more. So 40% time savings of 3 seconds isn't a huge deal to me. And most of the time .EXR's are much larger files which takes longer to write to disk.
Does that make sense? Or are you getting different numbers than me?