Hi,
On a project I was working on I found that the latency with DT-INTS-18 was 29uS at 20Mhz, that's 145 cycles. I measured this with the scope triggering on the external signal that was firing the interrupt and then setting an output high as the very first thing in the ISR.

29uS is is basically 30% of the time when interrupting at 12kHz then it takes roughly the same amount of time to restore all the registers when leaving the ISR.

Now, this was with the ISR declared as a PBP handler. I now see that you have the handler declared as an ASM-handler (but still written in) PBP. This makes it quite a bit faster since DT-INTS doesn't save the PBP system variables. BUT because of this you need to be VERY (I mean VERY) careful about what you do in your ISR if you declare it as type ASM but writes it in PBP. In THIS case it may not matter since you aren't doing anything in your main routine but once you start to add stuff there AND have an interrupt handler using the system vars without saving them you are in trouble.

I found that an interrupt declared as ASM with the DT-INTS has a latency of around 40 cycles.

You can read about my findings in this thread.

/Henrik.