I would not agree.
The higher CFM will just overload the lower fan and force it to work harder than it's meant to, while the lower CFM fan will introduce resistance against the higher fan and in turn make it work harder than it's supposed to.
This is why you need the same fans both sides. It's not just about setting RPM, as you need the same static pressure and airflow values, as well as flow characteristics. Otherwise they're just fighting against each other. At best, it is inefficient and you get all sorts of weird airflow interactions and annoying noises, and at worst you might damage your fans.
For example, if you have a fan with a wider airflow spread pushing in, that will slow the air and the pull fan will have to work harder than it's designed for, which could result in damage. Similarly, if you have too narrow a spread coming in, the airflow will batter off the pull fan, before creating a compression stall, and then batter back against the push fan, which is even more likely to damage them. In extreme cases this could blow the bearing and spray fluid over your components, or potentially snap some fan blades off and fling those around inside your case.
Thanks, that's useful. I'll order a couple of extra Arctics so the rad has the same gear on both sides before I start on the profiles - can just move the fractal prismas' to case exhaust duty.