Before we got FTTC I used to load balance 2 ADSL connections with an pfSense router as we struggled with only 8 mb connection, at one stage I had Zen and PlusNet. PlusNet was good, fast connection and uptime but the moment I had an issue it was impossible to get support, ages waiting on the phone .. terrible, unlike Zen who are excellent support-wise in my experience.
I love the idea of a mega-fast connection but with 4 adults we manage fine with one 80/20 connection, no complaints. Especially with Zen's 'Price for Life' promise (now not available for new customers but still valid for old customers) its very hard to justify changing.
C