A lot of that 30bhp is negated by the extra weight, it's 75 kgs, a bit like carrying a passenger. 0-60 times will vary considerably depending on the driver too, an expert will know exactly the revs and clutch release speed, he or she will know the precise moment to change gear. If you look at the claimed figures they suggest a 0-60 time of either 5.7 or 5.9, just depends which review you read. If you read some of the road test reviews, ie those magazines who have actually taken the Zed to a track and accurately measured the 0-60 using calibrated equipment then the times vary from 5.3 to 6.2 and anything in between. I would suggest that on an average road using road tyres and half a tank of fuel only a few of us would break 6.5 seconds.
It's not just The Zed though, I looked at performance figures for some of the cars I've owned in the past and they vary considerably.
Pete