I believe the 1D has less weight because of the fact that there is less gas tank so, it seems to accelerate better at low speed than the 1A at times only because the 1A may be carrying more fuel.
In the end I like the slightly better top speed of the 1A and the fact that it has the wing tanks; I almost never get shot down from a fuel leak.
The 1D does have 50 more rounds of .50 cal. though.....