I did my own little back to back with Marko_R1 about 3 years ago on his RB30 with -10's. We went for a drive and a 4th gear pull up a hill down the road from my place it shuffled it's brains out. Put the pipe with the divider on the car and did the same drive. I reckon it was a 90% improvement. Funnily enough, I bought that pipe back off him and it's now on my car.
Definately a little cheeky mod to do, that doesn't cost much and does make a difference!