They atomise better because there is greater airspeed through the primaries at low to mid throttle. Higher airspeed = better atomisation and conversely better throttle response (one of the reasons a 2bbl 253 is often quicker 80-100 km/h in second than a 308 4bbl in an equivalent chassis). When the revs get up the 4bbl comes into its own.

Have seen plenty of people remove their quaddy off their 308 everyday driver (I've done it myself) and fit a 600/650 Holley, only to return at a later stage to refit the quaddy. They are a fairly well suited carb for the 308 as long as they are set up right. The small primaries work well for economy around town and the cavernous secondaries are good enough to feed a 400 small block. They flow in the region of 750CFM (in the Australian ones), there were some larger ones fitted in the 'States that flowed 800CFM which are identified by a slightly different venturi and progression port design.

They really only start to get stretched on a Holden engine when you start looking at a cammy, ported VN headed 383ci. But take it to a bloke who knows exactly what he is doing with them and you'll never have another problem with them.

(Hint): if your running one you intend on keeping for a long time, hunt down a few spares for them NOW. Secondary Vac brakes (common issue) are getting very hard to find as I'm not too sure they are still making any in the 'States anymore.