I have a GE 1.5 VTi manual.

I get somewhere between 5.9 and 6.7 depending on where I go and how I drive.

I mostly use E10 or 91, but have tried 95 for a couple of tanks. My results from this are inconclusive so far, and I'm reluctant to spend the extra 13c/litre to find out based on the evidence I've seen so far.

I have had the airconditioning on most of that time.

I test drove a 1.3 auto and though the performance was OK, I doubt you'd improve much on the above figures because you need more right foot in the 1.3 to go places, especially with a load on.

If most of your driving is in the city and alone, the 1.3 makes a powerful argument given the price difference. It still matches the performance of most of it's competitor's 1.5s