I've been happy with O2's customer service and line stability, but the best I've managed to sustain speed-wise from them has been around 5Mbit/s down and 1Mbit/s up. Suffice to say, now that BT Infinity is enabled in my area, my intention is to move to this shortly, as I should then get nominally up to around 59Mbit/s down and 20Mbit/s up.