When you apply Canon software's Digital Lens Optimizer and save the results to the RAW image it massively increases the file size. A 5D Mark III file with a lot of bright features is already fairly large. The original file I'm dealing with today, out of the camera, would be about 39 megabytes. After applying DLO processing the file size jumped to 71 megabytes.
It's no wonder my Photomatix Essentials HDR software struggled dealing with 5 bracketed files that size on my 2010 MacBook Pro. As it turned out, I didn't like the results of the Photomatix processing and I used Canon's DPP software which is limited to 3 files for HDR processing.
I used the normally exposed image and images exposed 2 stops under and 2 stops over the camera's normal exposure. There was no hand holding this time as the normally exposed image was 1/30th of a second which made the 2 stop over exposed image 1/8th of a second. All images were made with the 5D Mark III, EF 70-200 f/2.8L USM lens with polarizer filter at 200mm, f/8 and ISO 100. I used live view to reduce vibration and, of course, a tripod and cable release.
By saving the JPG after HDR processing at the highest quality I had a 26 megabyte file I could crop for better images. By saving those cropped files at the highest quality I ended up with 4 files ranging in size from 2.3 to 4.6 megabytes.
These images are all reduced to the 1200x800 file size I use to post on this blog.