1> What is the maximum size they will get to if I were able to download the complete files?
OS 1:25K Full GB is 8.6GB in .QC3 format, OS 1:50K Full GB is 2.2GB in .QC3 format, and OS StreetView Full GB is 9.9GB in .QC3 format
2> What is the maximum size of the qc3 file that can be used on the A2800? (I note that Street view is very slow in loading).
4GB is the maximum file size on the Adventurer 2800 that we have tested.
3> What is the best Micro SD card to use?
The Adventurer 2800 can use micro sd cards up to 16GB. I cant say I have seen any difference between the makes of cards for data transfer speeds.