Oops... failed to note the smaller drive size.
Looking at your link, I see this SSD is actually pretty inexpensive, but it's Multi Layer Cell (MLC) flash memory so a touch more error-prone and slower than Single Layer Cell (SLC) would be. It is compatible from what the info on the seller's site says, too. Heck, at that price, cheap enough to try and not lose sleep over if it didn't work.
Pity they don't make PCMCIA flash memory of any real size (the X40 has two slots, right?). I did find several PCMCIA dual ESATA interfaces, though... at Newegg.