per your question on what QS models have the 128GB HDD limit:

there was once one page on this site, which listed the part numbers of the logicboards and the specific models in which it was put in.

I remember that page had all info one need at first to get started with OS 9 installation. It had a picture of a coffin and a HDD with an orange 9 on it and other nice icons.
I don't know, where that site has gone, but there you would find the answer.

Also, the reintroduced Single 1,25GHz MDD of 2003 was available BTO with DP 1,25GHz and still OS 9 bootable, would that very last DP model (without FW800! Though 2003) have the L3 cache, too?


Edit: found it differently and in another place:
QuickSilver 733, QuickSilver 800, QuickSilver DP 800, QuickSilver 867, QuickSilver 933, QuickSilver Dual 1 GHz with logic board 820-1342-B (QS logic board 820-1276-A will NOT work and peak out at 128 GB),