I got the Kingston 8GB 1066Mhz (since my MacBook is a year earlier) and all I can say is it runs like a champ! I went from 6gigs to 8 and multitasking is awesome! Literally had compressor doing a multi pass blu-ray encode, ripping a DVD with handbrake (2 pass), safari open with 5 tabs, and all this was while I was editing a short 720p video in FCP X. But to answer your question I think you would need to test it out yourself...everyones machine varies...I have dual hard drives in (a 5400 and a 7200) and I don't feel like my battery has drained more than normal...I do run allot of CPU intensive apps nearly all the time though so I keep it near a charger most of the time. If on a rare occasion I am doing something casual like browsing with 3-4 tabs I get 4-7 hours...my first laptops battery was like <2 hours so I don't complain.