I suspect in Enemy Coast Ahead, the groups with the ability to take the G-2 will do so, because they specifically registered for those groups vs. the ones that have only the G-6 as a choice.
But, to discuss the merits:
In Battle Over Germany, we were flying around at 34k, where the P-51's and P-47's were 90 mph faster than we were in our G's. Whether we had a slightly faster, slightly better-turning G-2 didn't matter on that scale, so we went with more firepower. The G-6 is 1.3 times as lethal as the G-2 in firepower.
In Enemy Coast Ahead, the most-numerous opponent is the Spit 9, with performace very close to that of the 190G, so the bit of extra speed and turning for the G-2 could make more of a difference. So there, it's a harder call. More firepower doesn't necessarily trump slightly better speed and turning in that situation. I think either choice is a decent one there.