aucatc,
most of Europe uses the 4DME principle. Many times there's a NAV AID (a marker) just there... And as others stated, 160kts is also a widely recognized speed control down to 4DME, when traffic hits your face...
More or less the 4DME speed control comes from the ICAO rule - no speed control after passing 4DME from the threshold.
(let's forget about wake turb. separation and meteo conditions for a while)
Now, if you need 3NM separation all the way to the threshold, you should try with a "buffer" as mentioned. Maybe 4, 4.5NM and locked on 160kts 'till 4DME?
Different type of aircraft can also be funny... A good turboprop with it's 200+ until 4DME can "run away" or "close up" if you really need. But should be done with pilots concurrence and not by default. A320 family with CONF0,1,2,3,4 is also known to be able to reduce significantly on final approach phase. Not very professional to force them anyway...
Spitoon as well wrote about the "reduced visual" after 4DME. Depends on your rules of course.