Having just switched web hosts, I now have the ability to run my site on PHP 7 (my former host wouldn't allow me to have some sites on PHP 7 at the same time as others that were still on 5).
So, does it matter whether I choose 7.0, or 7.1 or 7.2? All of those are options in my PHP manger.
Each new PHP version has some fixes and improvement in code structure or performance. For example, there was a huge difference in performance between 5.6 and 7.0 but only slight improvement in performance between 7.0 and 7.2. I have used PHP 7.2 on my Cloudways hosting server. They have a custom stack that consists of varnish, memcached, redis and php-fpm. I upgraded directly from 5.6 to 7.2 and noticed a huge difference in performance. My website used to load in 2.2s but now loads in 1.1s.
Everything except PHP 7.2 is end of life 12/31. Go 7.2x
That's gonna depend on what version of cs-cart the merchant is on. Only more recent versions ( don't trust my memory) like 4.7 and up will work properly with 7.x without modification.