So one thing the RTL test utility does not do is test the digital in / out ! Now that takes the converters out of the equation right? I guess I could test it by patching in my 01V.

 
Yes, that would take the A/D and D/A out of the equation...
But... you'd still have latency from the O1V's converters (or whatever converters you use).
No way to avoid it...
That said, the A/D D/A at most contribute 2ms to RTL... so they're not the biggest factor.
The problem with typical audio interfaces is the large/hidden safety buffer (of which you have no control).
 
BTW, Even if the audio interface provides low RTL, the design/drivers need to be up to the task.  Otherwise, the setting will be useless (glitches/garbled audio).

So one thing the RTL test utility does not do is test the digital in / out

It will if you can create the data loopback. My E-MU 1820m will do it via the Patchmix interface, and it lops 88 samples off the RTL. Just about 2ms like Jim said. All that's left are the buffers and another 8 samples for PCI bus I/O.

My idea of using the 01v was stupid once I gave it a little more thought! Whats wrong with this picture kind of thing. I'm afraid the solution is as always $$$$$$$$$$$
COme on you Tascam and M Audio users , still no feedback from you and I'm offering free beer downstairs!

dawbench.com tests interfaces for RTL

Warning: Ancient thread that probably does not need any more responses.