You do want some air flow restriction be the airflow restrictions govern how quickly the SU's pistons rise, and you want to match head and carb flow with the air filter presssure drop. This has a lot to do with the intake head flow an porting.
As far as the SU air filter set-up I described, picture a stock set-up for the HS6 model with a single air filter for each carb, you know the old yellow paper style with blue painted metal end caps? Make two K&N element housings to fit, but each element has about 5 times more filter area than the stock SU filter, thus has that much less pressure drop, which is a considerable flow improvement, especially at high rpm's.
As far as the CAI, if it is afixed to a 3 inch diameter tubing from the end where the filter is attached, the conductance loss through the long tube is adding to the pressure drop, AND the filter area is still less than one of the twin K&N's that I descrbe above. Any such tubing plus an air box adds conductance loss. If there's no air box, no conductance loss, just a slight pressure drop across the filter element. More filter area + less conductance loss = better flow. And yes it will sound very throaty.
If your concerned about heat from the manifold, instead of using the stock Volvo heat shield from a B18B (A MUST for running SU's open like I describe, along with the thick phenolic spacers), make up an aluminum plate that is wider than the stock plate and have it run under both carbs forwards like a tray to angle the heat backwards and down under the tray, while scooping air from the sweep of the fan. Kind of 'S' shaped, under, down and over. Polish it up nice and shinny for everyone to see. It works better that way, and it keeps the overflow gas from the side float vents from hitting the exhaust manifold when you run really hot, too........!
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'89 245 Sportwagon, '04 V70 2.5T Sportwagon