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I think you're a little out of date - "barely producing current at tickover" is more worthy of my long gone previous employer - the Prince of Darkness.
Alternators now produce significant current at idle - the 120A Valeo machine on my VAG PD will manage almost 50A at about 950 engine rpm. This is because the speed range on a diesel is restricted and so the machine can be geared more highly without overspeeding the rotor. Diesels also tend to have a higher idle speed.
As the current/speed curve is very steep at this point in the machine's operating map, a small speed difference causes a large change in the available output. The choice of machine for a given frame size is not straightforward and depends on drive ratio, speed range and load characteristics.
Unless you blaze down a motorway with everything switched on, my recommendation would be to fit the lower output machine provided it is of the same magnetic dimensions. Many producers fit a shorter stator to the low output versions.
The VAG PD of my year and body can have a 120 or a 150A Valeo machine. They're the same physical size and the 120A machine gives considerably more output - when you really need it. Above idle, unless the load is huge, the machine will immediately hit the regulator.
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