Hi Scott.

You're correct; 160 cfm isn't going to cut it.  But with 1200 cfm to play around with, you should consider enlarging your booth to about 3' X 3'.  For a regular back-drafted booth, it would give you a face velocity of around 120 fpm.  At 2.5' X 2.5', you would have a face velocity of around 190 fpm.  Either way, you'd have enough velocity available to account for the resistance from several filters, and to provide enough velocity pressure to exhaust your vapors outside.  Remember, the 80-100 fpm face velocity is the MINIMUM recommended airflow. 

In a downdraft booth, the recommended velocity is less because you're relying on gravity to help capture the vapor fraction from your paint.  A much slower velocity is also an advantage if you're planning on passing the exhausted air through a charcoal filter with the intention of putting the exhausted air back into the room.  If not, then you should still be OK with the higher velocities.  You should consider mounting the fan within a plenum a few inches below where your kit will sit, and using a small baffle plate in front of the fan to help evenly distribute the airflow.  The base where the kit will sit during painting should also be evenly perforated for the same reason.  With higher airflow rates, you'll also have to make some minor adjustments in the way you perform airbrushing (move closer, more thinner or retarder to lengthen drying time, etc.).  Nothing insurmountable in the least.

Oh, yeah (Thanks, brain!).  Get the 1200 cfm fan and connect it to a rheostat switch.  You now have complete control over the amount of airflow you wish to supply to your booth.  This type of setup is not unusual; I see it in prosthodontic (dental prosthetics) labs regularly. With 4 square feet of face area, and 1200 cfm, you have plenty of wiggle-room.

If you're still unsatisfied with these suggestions, I would recommend you shop around and try to find a fan with a lower cfm rating. 

Keep us informed on your decisions, and send some pics when you get your booth completed.

Hope this helps you some.

Gip Winecoff