First, It depends on how a perticular codec is supported weather or not it will use more power to decode or not, Higher bitrate will take more power to decode then lower(flac vs ogg for example) but thats a different topic.
Vorbis(ogg) on some players KILLS batt life, on others like the fuze, you loose at most an hour or 2 of batt life(my testing the WORST I loose is 1.5hr vs using MP3 files)
Vorbis using aotuv’s latest encoder could likely give you audible transparency at q-2 or q-3, only rare tracks take higher when using the latist aoTuV encoder, q-6 is considered transparent on all but a few “killer tracks” (tracks designed to cause problems)
Note MPC uses less power to decode then mp3, but isnt currently supported by fuze or any other sansa player either.
My advice if you want to carry around your pod casts or whatever that by default come in MP2 format, convert to vorbis and toss them on your fuze, They will use less power then the FLAC your already using and you will be able to fit more of them on the player.
I use vorbis because no other codec I have found has the quality to bitrate that vorbis encoded with aoTuV’s encoders offers, and Im sorry but carrying around a few flac’s on a portible player is silly, it eats batt life, the players also tend to have a lower snr then a good set of IEM’s or cans(the cans would likely also have pretty high resistance so u would need an amp) when it comes down to it, Ogg just makes sense for these players, it decodes fast, offers excelent size to quality ratio and has plenty of encoders to play with(dbpoweramp FTW tho)
Oh and this isnt a one off with only loosing a little bat life, my samsung yp-u3 lost around 1 hr moving to ogg from mp3.
Ogg can be decoded MANY ways, there are a few common ways, but there are also alot of less common decoders written to be optimized for specific player hardware, samsung and sansa and cowan and archos tend to do a decent job on newer players when it comes to their decoders being well optimized to use as little power as possible and still maintain excellent sound quality.
alot of cheaper players use…far less optimal vorbis and/or flac support that ■■■■■ even more batt life, I have seen some cheap asian players that had their batt life cut in HALF by using anything but mp3(not kidding, its really that bad) then again i have seen some asian players that had BETTER support for non-mp3 formats then they do for mp3, for mainstream players like the fuze/clip/exct the diffrance in batt life shouldnt be very large these days, I know Im not gonna go back to mp3 over ogg for my 8gb fuze(with 8gb card) I like being able to fit lots of music and audio books onto my player without having to resort to my stuff sounding like it was recorded in a toilet bowl 
