So, just say no - click cancel or whatever, do "no operation", when windows asks to format the card.
I'm not sure about the download rate, but it's on the order of 1 minute real time to download 10 mins of raw log data over serial at the higher speed.
There is no possibility to delete single logs, maybe if there is support for a proper file system later (eg FAT like everything else that's "pluggable").