Gmail is also better on Froyo. It has some better features, including a snapping header, making it easier to star and reply to messages; you can select and copy text in a message; you can have notifications for individual messages rather than a single notification until you enter the app or clear the notification out. (In other words, 2.1 and earlier would notify you once when the first mail message hit your inbox, and would not vibrate or sound again until you cleared it, even if you received several messages.)
FWIW, battery life on kaos froyo is no different than any other ROM I have run. They are all pretty much the same for me.