Miraz
I have only had the LS800 to 10k but I generally fly around 9 or 10k. The only problem I have had is occassional overheating, because the LS800 does not have a cooling fan. That problem is now solved because the RamMount people have released a cooling fan for the RamMount mounting for the LS800 that plugs into a USB port on the LS800 - works a treat.
I like the Jepp FliteDeck. Among its many features, it is useful to have the position of the aeroplane displayed on the Approach Plate while flying an approach.
If you don't want all of the features of JeppView and FliteDeck, but just want GPS position to display on electronic charts, then Fugawi is useful.
FTDK