Looking at a glance;
* over 6k alt the Bf109G-6 on WEP, is about the same in speed, as the Bf109G-2 on military power(100% throttle, no WEP).
* the climbrate and acceleration is roughly the same.
* maneuverability, at least in terms of turn circle, is (contrary to popular belief), is also same. According to my testings;
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Turn time, turn speed, and turn radius.
-first figure is for normal flight,
-second figure for 1 notch of flaps,
-third figure for full flaps
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Bf109G-2 (1.0/1.2/1.2)
- 17 seconds (167mph), 202.1m
- 18 seconds (160mph), 205.0m
- 17 seconds (148mph), 179.0m
Bf109G-6 (1.0/1.2/1.2)
MG151/20
- 18 seconds (163mph), 208.8m
- 18 seconds (160mph), 204.9m
- 18 seconds (134mph), 171.6m
MK108
- 18 seconds (168mph), 215.2m
- 19 seconds (158mph), 213.6m
- 18 seconds (137mph), 175.5m
However, it is possible the Bf109G-6 might feel a little bit 'heavier' when maneuvering with MK108 30mms on board.
...
Therefore, it basically comes down to individual preference.
In the MA, IMO "350mph at deck" is roughly the "lowest point" to consider a plane really powerful and competitive. When a plane can do over 350mph, preferably over 360, it can afford to fight enemy planes aggressively at low altitudes, but still can manage to escape with a bit of SA when things get hairy.
The P-38L and the Ki-84-Ia manages 344mph at deck, and these two are the "last in line" for "MA-competitive" fighters, being able to duke it out in aggressive combat, but still enough to outrun most enemy planes... and perhaps escape to safety with good timing. (although both will never outrun the real speedsters..)
The Bf109G-2 and G-6, unfortunately, is little bit slower than those two planes. While it is capable in the hands of a good pilot, and will be able to fight any plane at almost equal terms, still the lacking speed performance will often limit the pilot to fly with a minimum "safety margin" in mind. It can't really commit to a fight when there are multiple enemies nearby.
So naturally, be it Bf109G-2 or G-6, both will be caught by faster enemy planes pretty easily if it loses an important alt advantage. The Bf109G-2 is faster than the G-6, but in the MA that difference isn't by much.
Therefore, at least in my case, I will prefer the G-6 over the G-2.
In these 109s, against the MA competition, there is no choice but to keep flying SA-wise all the way through the sortie, and the small performance advantage of the G-2 isn't really up to much.
So, naturally, for me, the firepower comes first - one pass, one shot kill with the 30mms; this is much more important for me than being 6~8mph faster, or little bit lighter maneuvering.
Even if you are in a G-2, you won't be able to outrun the D-9s, G-10s, P-51s, Typhs and etc... even if in a G-2, you won't be able to outtrun Spitfires. However, if you are in a G-6, little bit slower but quite simular characteristics, unlike the G-2 the G-6 CAN kill an enemy plane with one good shot.
For instance, you may be able to duke it out with an La-7 in a G-2 or a G-6.. but however, in a G-2 you may land some shots on the enemy plane but it will not go down. But in the G-6, that one shot, when connected right, will kill him on the spot.
So I prefer the G-6 with 30mms.