ABout 50 channel GPS:
"50 channels like ublox some people say that is less than 2 meters of error. (but letter this GPS is going to be more accurate, because is build in with the new GPS technology called Galileo from Europe: Galileo (satellite navigation) - Wikipedia )."
i mean someday we gonna have more satellites , so ublog is a good investment for the future 
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Nice, can you share your altimeter??? just to see.
I thought about pitot tubes, but is difficult for me ;D. So maybe with ground speed is enough, because the average of time ill fly in straight line, not making acrobatics.
About your altimeter you need a temp compensation maybe? About my altimeter i don't want to reinvent the wheel, so ill use the sparkfun altimeter with temp compensation ;).
Read this, maybe help you: