FWIW, ALINES() is a lot faster. GetWordNum() is great if you just need to pull one or two words out, but if you need all the words split, use ALINES().
Here's what I wrote about the speed issue a while back:
"These two functions are really designed more for extracting specific words than for parsing whole strings, though. They’re much slower than ALINES() and even slower than manually parsing with AT() and SUBSTR(). Like manual parsing, the slowdown is much more than linear. In my tests, parsing a 160-character string into words 10 times with these functions took less .01 seconds, but for a string of more than 80,000 characters, 10 passes took more than 100 seconds. By comparison, using ALINES() with the optional parse characters, the time went from about .001 seconds for 160 characters to .08 seconds for the 80,000+-character string."
Tamar