Interesting question. I seriously doubt that wince can read exfat. Even if it can, with an 8gb sd card, you would not be able to enjoy many of the advantages, but most or the dissadvantages, like...........
"The standard exFAT format only uses a single file allocation table and free space map. Previous FAT used alternating tables, as this allowed recovery of the file system if the media was ejected during a write (which occurs frequently in practice with removable media)."
Faster shouldn't be a concern as long as the sd card is fast enough to deliver the data when the system needs it. For the most part a class 4 sd card is more than fast enough to get the job done. Personally, I'd opt for fat32 and redundant FAT tables. It not like your going to get to your destination any faster because your using exfat.
Another thing you should be concerned about, is whether your desktop/laptop pc is capable of writing to an exfat sd card without corrupting it. I know mine are not setup to support exfat.
If you really want to get anal about it, read through this. I think you'll find that exfat has no real speed advantage over fat32 when it comes to reading from an sd card.