Filter and CFM Question

I know, I know. Been blowing this place up... sorry. So hopefully my last question.

Went deeper into what filter to get for when I replace my system and noticed the CFM and pressure stuff.

Current system to be replaced is constant 1600 CFM fan with a 16x25x1 filter. Filters say they are rated for up to 1350 CFM.

New system is viable speed, but max speed is 1600 CFM also but takes a 20x20x1 filter in its internal cabinet. When I looked I couldnt find a decent filter with more than 1300 CFM.

I want the AprilAire 20x20x4 with the 13 merv rating but they max out at 1200 CFM.

Do I need to upsize to one of the AprilAire 20x25x4 that max out the CFM at 2000?

My worry is if I dont, I will suffocate the blower and have to much static pressure, but if I upsize to much then I wont have enough static pressure. If I upsize I know I wont get the full airflow because I will need to neck it down to fit the air handler.

Thoughts, suggestions?