Thanks for the update, I've updated the UKHAS Wiki with your information. Generally people doing HAB launches anyway are using the uBLOX 6 now due to the performance, power etc. In fact I'm half considering doing a custom Trackuino board with one on it. Although not pin for pin you can put a ublox module in place of the Venus quite easily.
For any one coming to the party now we (at least in the UK) are recommending the ublox chips, in fact at least 6 out of the top 10 highest amateur launches in the world have used them.
The MTK3339 does on paper look interesting but I only know of one launch where it didn't work properly, this may have been misconfiguration though. I agree it does need testing however they have been largly overlooked as the performance of the uBlox is so good people just aren't looking anywhere else (at least within UKHAS).