One of my SDIs tests at 0.3 smoke level on emissions.... better than many brand new diesels! The wierd thing is that if you look on the compliance plate/sticker in the engine bay, it says 0.7 is the limit. UK MOT tests the level to 1.5 I think (or is it 2.5 smoke?), but they are "meant to" test to the compliance plate limit- if visible. NOX still isn't part of testing, but I'll be very interested to see what levels our diesels chuck out when/if it ever comes in. EGR is disabled on all mine (and gas flowed/ported), so technically NOX should be quite high when the engine is cold. But in the current MOT, they only check exhaust gases when the engine is hot, so I can't imagine the test ever failing. But what do I know about this nonsense... (not much).
There is something called a "blue angel" cat that you can fit to an SDI, which apparently brings down emissions to almost clean air (other than the CO2).