I had better success with setting my tent up with metal shelving that went from floor to ceiling and using a "hot/cold aisle" approach. The intake is in front of the shelves and all the fans blowing towards the back of the tent. The exhaust fans suck from the top of the tent directly outside. I also used styrofoam insulation boards on the front of the shelves to block off unused space so it forces the airflow directly through the rigs.
4,500CFM is solid, are you bringing air from outside in and pushing it back out without restriction? If you don't have airflow to/from outside then you will restrict air movement. Bringing in air from outside and pushing hot air out made a significant difference.
Before the tent I had metal lockers working the way you describe, which is similar to how rackable servers work - intake at front, exhaust to the back. This did the job over the winter but temperatures were different. On each of these I had 2 compartments of 13 GPUs each with 8x50cfm 120mm PC fans at 12V for intake at the front and 2x 200mc/h duct fans for exhaust at the back of the locker. It worked nice (all GPUs under 50C) until spring when temps started spiking over 70C in the locker contraptions so now I am playing with tents.
The tent I am trying now has the intake fans at the bottom and the exhaust at the top, I figure hot air should rise anyway because physics and I also have 6 duct fans inside blowing from bottom to top. I've tried every possible combination of all these fans on/off, switched positions and so on... I figure I'll just have to try some AC because right now the GPUs mine at some 65C during the day and 55-60C at night...I am not comfortable perma running them at ~60C, I'd rather have 50 or 55 max.
Are you venting your hot air outside from the output of exhaust fan(s)? Also, are you bringing in air from outside on the intake side? That is what made a big difference for me.
I am jealous of your temps. I live in Austin, TX and in the summertime it gets brutally hot here.