To solve the problem of my Apache server log for some domains
exceeding the 2GB filesize limit, I've recently added some extra
directives to httpd.conf to log images to a separate log.
Below is the original entry (CASE 1):

CustomLog domlogs/the-domain.com combined

Then I've added the "images" directive (CASE 2)

SetEnvIfNoCase Request_URI "\.gif$" is_image=gif
SetEnvIfNoCase Request_URI "\.png$" is_image=png
SetEnvIfNoCase Request_URI "\.jpg$" is_image=jpg
CustomLog domlogs/the-domain.com.images combined env=is_image
CustomLog domlogs/the-domain.com combined env=!is_image


I was considering dumping the images log altogether and set the directive (CASE 3):

SetEnvIfNoCase Request_URI "\.gif$" is_image=gif
SetEnvIfNoCase Request_URI "\.png$" is_image=png
SetEnvIfNoCase Request_URI "\.jpg$" is_image=jpg
CustomLog /dev/null combined env=is_image
CustomLog domlogs/the-domain.com combined env=!is_image


Question 1: 
I'm worried that CASE 2&3 will consume way more resources because it
has to do a REGEX for every query.
From resource consumption point of view, how will each of the
different cases (CASE 1-3) differ from the others and will the
difference be significant enough to be worth paying attention to?

Question 2:
Is there any other way to make it more efficient?