UPDATE: 64GB micro SDXC card DOES work in LG Optimus 2x
I tested 64GB mircro SDXC in my LG 2x (Modaco rom Gr6 and HP 2x kernel RC12-R) and it DOES NOT work
I was able to format the card to FAT32 in the phone, but when I try to mount it, the phone restarts itself.
If anyone else has different experience, please share.
BTW the card is SDSDQY-064G-U46A
I managed to fix it. I'm not sure which steps were actually necessary but just to be sure I list them all.
First I tried NicomUA's idea of splitting the patritions in two 32GB. For that I used Paragon Partition Manager 11 Free. And IT WORKED!
I made two partitions. I was able to access the first one in the phone, but I could not format or edit the second one neither in the PPM anymore.
So I used SDFormatter 3.1 and reformated the card into its original state with option "Format size adjustment".
Then I checked the partition structure again in PPM. It was exFAT, but with 16MB free space at the beginning.
I formated it to FAT 32 and resized it to 32GB (Now I made only one partition and left the rest of the space unallocated). It worked in the phone.
So I tried to resize the partion to see how far I can go. 32GB worked in my phone. 33GB worked in my phone! And suddenly whole 64GB worked in my phone!!!
I filled the card with movies and music to the max and tested if I can really access the content and YES, I was able to play anything on the card!