You are right about the RSP/RDP distinction. My point is that removing transistors from one chip doesn't magically let you add more transistors to another chip, that's not how IC fabrication works. And the CPU was not a custom design, it was a VR4300 licensed by NEC from the original R4300.

Anyway, the real problem is that TMEM was not a hardware-managed cache, but a scratchpad RAM fully under the control of the programmer, which meant that the whole texture had to fit under a meagre 4 kB of RAM! It is the same mistake that Sony and IBM later made with the Cell.