BobxMarley, did you solve this issue?
I have the exact same problem 
CF 9 on a Mac OSX server, with Unix.
Trying to import a excel spreadsheet with 10.000 rows and about 15 columns.
It runs very fast up to about 6.000 rows, then it slows down more and more until it stops, and then I get a 500 error.
First I hade the entire loop within a cftransaction, but I've also tried to have the cftransaction inside the loop.
I have about 4-5 sql queries within the loop that puts the data into different tables.