There is no downside.
Matt is ALWAYS the better choice.
Aperture or Lightroom are your 2 choices there. I'd personally say go for Lightroom since it ties in with all the Adobe products and works on windows on mac so if you ever change or need to work with your stuff on windows, you can export your catalog etc. to migrate to another computer.
Battery life shouldnt be a big issue on macs they tend to have half decent batteries. Granted dont expect 6 hours of photo editing out of it though, 3 if your lucky and its one of the newest ones with the new type of battery.
Canon EOS 5DmkII + BG-E6 + Canon EOS 40D + BG-E2N + Canon EOS 33
Canon 17-40 F/4L
USM + Canon 24-70 F/2.8L
USM + Canon 28mm F/1.8 USM + Canon 70-200 F/2.8L
USM IS + Canon 85mm F/1.8 USM
Canon Speedlite 580EX II + Canon Speedlite 540EZ + 2 x Nikon SB-80DX
Cactus V2s Wireless Trigger - 5 x
Cactus V2s Wireless Reciever