I input TIFFs to keep up the quality and output TIFF as well. Finished TIFFs were between 150-300+MB.
I tried to use 4.9 on a faster SSD iMac but it crashed repeatedly on file #1.
I will need to do more experiments with 4.9 to see if there was a problem with my source files (they had been scans of old postcards I received then colorized online and returned as progressive JPEGs; I then ran them through standalone Impression for some artsy and saved as TIFF, then did GP at 4x awhile ago with v4.4.5).
If I had used my own original JPEGs, I might not have had problem (?).
Here is an example of the artsy (reduced).