I can't speak for the 170, but it has made a difference on my 140, I expect it's a combination of the map as well, but on my 10 mile run to work I was averaging between 42.5 - 47.5 mpg, on Monday I got 52mpg!!
That's a combination on 3-5 minutes on the motorway, and then twisty A roads.
The thing to look at is the EGR, is an efficient bit of kit up to about 30k (normal driving, servicing etc) after that it gets clogged which reduces performance and mpg. You could whip it off, clean and refit, but if you are going down the route of DPF delete and remap you may as well invest the 70 sheets and get the EGR bypass also.
Something to bare in mind, removing it will increase emissions but they will still be way below the require for UK law.
I was looking at FR tuning, but was put off by reports of shocking customer service and wrong parts supplied, perhaps just an isolated incident, but the boys at Darkside are the nutts.