I installed the i-Plate this evening. No real improvement in sync speed. However, my line attenuation has dropped by a tiny 0.5dB.
BUT...the big thing that I have noticed is far fewer errors recorded by my ADSL modem. I am using DMT Tool to monitor these errors. Web sites seem to load much faster too although that might be because of a placebo effect. So, the only hard data I have is that FEC errors are greatly reduced. I've only had the i-Plate installed for a couple of hours so i'll keep an eye on the errors over the next few days.
I also loaded up Rainbow 6 Vegas 2 on my Xbox 360 and searched for multiplayer games online and got a pageful full of 'green pings'. I've never had that before. Perhaps it was coincidence. Online play was silky smooth with no lag. Again, I could have been lucky but I'm of the opinion that it was a tenner well spent.
One thing to bear in mind is that when you take the faceplate off your master socket, ensure there is enough cable slack to fit the i-Plate. You need around 3 inches of cable slack to easily manoeuvre the i-Plate into position.