Let me also add some personal thoughts. Over the last decade or so Automatic transmissions have improved out of sight & these days it is not uncommon to see an Auto returning better fuel economy than a manual (on the same model car)

As we are talking about an FD1 lets do a simple comparrison. At 100KPH in an Auto the engine is spinning over @ about 1800RPM whereas in the manual it is doing about 2700RPM. Therefore your injectors on the manual are pumping in more fuel at the same road speed, admittedly only a small amount, but it adds up over time. The only disadvantage with the auto in highway cruising is it only has to sniff an incline or slight hill & it will drop back a gear. This can be very annoying to some people, but they fail to realise that there is insufficient torque at that RPM to tackle any sort of incline.

In these days of ridiculous fuel prices I believe it pays substantial dividends to learn to drive economically & there is an art to it that is difficult to learn for some. It is not necessarily a matter of driving slower, but leaning how to do it. A classic case is when my wife drives our CU2 Auto she uses about 3L/100k more than I do, yet I am the faster driver. Go figure that 1.