I had Infinity 2 installed by BT on Friday. Original estimate was for the full 80/20 as the cab is just over the road from me. Openreach guy was great, used the existing cat5e extension cable I had from the master socket to the cupboard where the rest of my network gear is, so no rewiring, although he did replace all the faceplates and checked the connections.
Currently using the HH3A (shame I didn't get the HH4), but planning on replacing with something else anyway as the HH seems to be lacking in the wireless range and reliability, ended up using my old Netgear 834pn as a WAP. I've investigated a few alternatives and will decide on one shortly.
Speeds are great, get the full download speed, just over 76Mbps, although upload ranges from 10Mbps-15Mpbs, I was expecting better, but I don't upload much, so not to fussed at the moment.
All in all it was a smooth operation, down time was minimal and I'm impressed with the speed.