Hard to say really - I don't bother keeping track of it as I only do very short journeys so I usually get something fairly awful.
The only time I was interested was the journey up to and back from P-Torque (Bristol -> Wolverhampton ->Bristol) and considering I was 'testing the goods' on the way back a fair few times, the MPG was virtually the same for both journeys.
I think the general consensus is that the MPG will generally at least stay the same or improve slightly with a re-map, but as you're more likely to put the boot in with the increased power (at least if you're a child like me) you'll probably find it drops a little.
Worth it though
The only time I was interested was the journey up to and back from P-Torque (Bristol -> Wolverhampton ->Bristol) and considering I was 'testing the goods' on the way back a fair few times, the MPG was virtually the same for both journeys.
I think the general consensus is that the MPG will generally at least stay the same or improve slightly with a re-map, but as you're more likely to put the boot in with the increased power (at least if you're a child like me) you'll probably find it drops a little.
Worth it though