Having played with Caterham Sevens of varying power outputs for the last 25 years, both on the road and in competition, I don't think any Seven owner would not consider having a bar. In fact the Lotus Seven club will only allow the competition height bar for cars, on their own track days and competitions, which must have a clear 2" between the top of a helmet and the bottom of the bar.
The big problem however is how to avoid damaging your head on the bar, but the likes of Demon Tweaks sell special dense foam 'lagging' which when put in the vicinity of driver and passenger heads will at least give slightly less of a headache, and allow one to at least have a better than average chance of survival or serious injury.'
