We regularly use Sys_CompareText to compare data grids and these files can get pretty big. I tested this out with a 152KB text file and it passed without a hitch. You may want to take a look at SYS_VerifyText, with this, SilkTest will allow you to open DifferenceViewer to see the differences in the file.
Hope this helps...
Steven P. Blunt
Software Automation Technical Lead
NASG Sales Force Productivity