I've been told to go min clean, which is fine, but what about these exact 180kts and 170kts to 5 miles etc, e.g. Today Flap 1 was 185, does it make a big difference? I've heard the +/- 10kts being mentioned but also heard that isn't the case, and with the enhanced Mode S, can some of the radar controllers see what speed we've selected on there?
You should fly the speeds as closely as possible. UK AIP textual AD data refers (eg for LL section 2.22 Flight Procedures 3) iii).
If you wish/need to fly a slightly different speed just advise when asked to maintain a particular speed. The exception would be on final app where we could do with knowing before vectoring you .1nm over the vortex gap behind something else that you can't do e.g. 160 to 4.
The mode s shows us the aircraft's IAS as of the last radar interrogation, not the selected speed - so there's no cheating!! We do see MCP selected level. We can also see aircraft-derived ground speed, and mag heading. If we 'hook' the aircraft we can also see aircraft ID, ROC/ROD amongst others - see here:-
Mode S
Regards