no expert on this topic but not entirely sure about performance issues due to the speed of that sd-port in general... would be really happy if you could look into this a bit during testing your solutions ;D
[nemo@localhost ~]$ df -h Filesystem Size Used Avail Use% Mounted on rootfs 14G 4.1G 9.2G 31% / /dev/mmcblk0p28 14G 4.1G 9.2G 31% / devtmpfs 406M 64K 406M 1% /dev tmpfs 407M 268K 406M 1% /dev/shm tmpfs 407M 23M 384M 6% /run tmpfs 407M 0 407M 0% /sys/fs/cgroup tmpfs 407M 24K 407M 1% /tmp /dev/mmcblk0p25 8.0M 4.2M 3.8M 54% /persist /dev/mmcblk0p19 8.0M 4.1M 3.9M 52% /drm /dev/mmcblk0p18 64M 45M 20M 70% /firmware /dev/mmcblk0p28 14G 4.1G 9.2G 31% /swap /dev/mmcblk0p28 14G 4.1G 9.2G 31% /home /dev/mmcblk0p9 48M 7.5M 40M 16% /var/systemlog /dev/mmcblk1p1 60G 2.6G 54G 5% /mnt/sdcard2 /dev/mmcblk1p1 60G 2.6G 54G 5% /home/nemo /dev/mmcblk1p1 60G 2.6G 54G 5% /data/sdcard tmpfs 407M 0 407M 0% /mnt/asec tmpfs 407M 0 407M 0% /mnt/obb /dev/mmcblk1p1 60G 2.6G 54G 5% /run/user/100000/media/sdcard /dev/mmcblk1p1 60G 2.6G 54G 5% /home/nemo /dev/mmcblk1p1 60G 2.6G 54G 5% /data/sdcard