There is not going to be night and day difference between a GTi and Ed30. When you think about it this way, there is technically only 15% difference in power which really is not a huge amount. Aerodynamics will put stop to most of that when the speed is up and off the line, you are restricted by the same transmission and limitation to deliver power to the road.
In addition, depending who is driving, a GTi could well be faster than an Ed30. All it takes is to be changing gears too early/late to take any advantage away.
Remapped, this would probably be less likely. Mod vs Mod, ie full exhaust, filter, bigger intercooler and remap, it would seem that more can be made out the BWJ engine over the BWA. 260bhp-270bhp is a rough figure for a well modified GTi vs 320-330bhp for the same mods on an Edition 30. All of a sudden the 30bhp or 15% defecit is closer to 25%. However then there is the issue of power delivery, so perhaps the Ed30s power advantage would be reduced initially slightly more than the GTi due to comparative inability to deliver power to the road.
