The Doing Our Bit blog on military and family history research, from Victoria BC based Steve Clifford, has a post estimating when Canadian Expeditionary Force service files at Library and Archives Canada will be digitized.
Based on completing digitization by the end of 1918 the estimate is that 2016 will see work being done on surnames starting with G into the start of M surnames.
One of the by-products of the post's table of the number of surnames in the file for each initial letter, is an estimate of how far you need to go into an unindexed alphabetically ordered file, like a microfilm, to find a surname.
D is one-quarter of the way through, G one-third, K one-half, M two-thirds, and P three-quarters.
Here's the complete table.