The 7445/55 is a LARGER process version of the 7447/57.
At least the most recent version of the 7455 (there were quite a few as Motorola baby stepped to the 7457s).
The smaller process allowed them to add a bigger cache within the same space, and you'd probably say the 7457s are the more advanced chips right now (and they do support the L3 cache, in fact they support more than the 7455.)
Now Apple didn't include the 7457 in the current crop and elected to go with the 7447 (one without the L3 cache) because the 7447 was as fast as the 7455 with L3 cache -- and putting fast L3 cache with the 7457 would be more expensive.
Plus there might have been issues with the 7457s L3 cache.
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Anyways the 7447s have (512K SRAM on-chip L2 cache) and are supposed to be less expensive than the 7445s and probably quite a bit less than a 7455 with a lot of L3 cache.
So it would be a little strange to choose a hotter, bigger, more expensive solution (7455 with L3 cache) than one as fast or faster that's smaller, cooler, and less expensive.