I haven't been able to get more than about 47 MB/s in ATAPI Mode 5. This makes sense because ATAPI_ULTRA_TIM_1 is limited to a minimum value of 2 for TDVS and TCYC-TDVS. At 133 Mhz SCLK this is 15 nsec for each parameter.
This seems to put tcyc at about 30 nsec, which is about what I'm measuring.
However tcyc for ATAPI mode 5 is 16.8 nsec. I don't see any way to get close to this with the ATAPI_ULTRA_TIM_1 limitation.
I tried setting the ATAPI_ULTRA_TIM_1 to 0x101 but this causes problems.