Well I got a chance to drive a Celerio today, it was the CTV version (it has a 2 speed ancillary gearbox on it to allow a wider gear range) and is a true single speed ctv.
Yes road noise is there but better than a couple of similar cars in the same class, motor at low rpm is silent and easy to drive in those rpm's but that means you can hear the road noise as there is no motor sound.
110 kph is at 2,000 rpm
and on smooth roads makes for a very quiet ride.
Idle is slightly lumpy as you can feel the 3 cylinder beat but not hear it, steep hills the cvt runs the engine up to 6,000 rpm and adjusts the gears as needed motor becomes vocal but sounds good (I like 3 cylinder engines).
I left the lot with 6km/l on the gauge (engine had maybe 10 km on it) and returned after a short and not gentle drive with 16km/l and it was still climbing the longer I drove, I suspect returning economy in the 4l/100km range would be doable with little effort.
Seriously considering buying one, just want to test a few others to be sure.
Anyone know anything about the current Polo? dearer but combined fuel consumption of 4.5 l/100km and a lot higher torque.