hello,

i guess i wont be able to answer your exact question regarding altitude, but i do have a Zi8. Ive used on previous backpacking trips, thats what i got it for. i love the thing, i works wonderfully. the video quality is great (especially for the price) and it come with an HDMI cable so you can hook it directly to your tv and watch in HD.

the controls are a little odd to get used to but it doesnt take long at all. the mic works really well. my favorite part may be how big the screen is, its really a nice feature compared to the tiny screens of the Flips.

im not sure about the flips but the Zi8 comes with rechargable AA's which is nice cuz u can always buy some back ups at a gas station or wherever.

one complaint i have about the Zi8 is the zoom, its pretty much pointless, but its a cheap and tiny camera so they will all have an equally bad zoom (atleast in this price range).

if you are able to wait long enough and live near a target, you should wait until it goes clearance and they only have a display left, when that happens, the price is dropped 30% off the clearance price, i got mine for $57.

if you have any specific qs let me know. good luck

jake