A 140mm E-loop at 900 rpm moves more air (free) than PK series at 1500 rpm. There is no static pressure rating that is going to compensate for that. The graph below is for the 120 e-loop series, but compare the 1300 and 1500 rpm models.

It's the same fan, just 200 rpm less on the max.

*"The 1300 rpm model has 50% less static pressure than the 1500 model, so obviously it is massively inferior"*. Fortunately, this is not true and static pressure ratings can be very misleading. Ultimately, it is the amount of air moving through the radiator that does the job. Static pressure can help you estimate how much air goes through at a certain resistance level, but P-Q curves aren't common and trying to figure out how much resistance the radiator offers (in terms of mm H20) is a little elusive. All AIO radiators are going to be comparatively low in terms of resistance. Substantially better airflow will trump most any static pressure deceits. I'll send a PM with some other ideas.