Messerschmitt Bf.109G, German users, part six

Some versions of the G-6 and later Gs had the standard tail replaced by a taller, wood-structure tail unit and redesigned rudder balance protruding forward into the fin which improved greatly stability at high speeds. Firepower was greatly increased thanks to the introduction of the WGr. 21cm (8in) underwing mortar/rockets and the 30mm (1.18in) Mk.108 cannon. Some batches were fitted with aileron Flettner tabs to decrease stick forces at high speeds. A new radio navigational method, called the Y-Verführung (Y-guidance) was introduced with the FuG 16ZY.
Every subsequent version of the Bf.109G was a modified G-6 airframe.
In early 1944, new engines with bigger superchargers for improved high-altittude performance (DB 605AS) or with MW-50 water injection for improved low/medium-altittude performance DB 605AM, or with those two featured mixed (DB 605ASM) were introduced to the Bf.109G-6. The maximum speed of the Bf.109G-6 was 530 km/h (320mph) at sea level and 640 km/h (391mph) at 6000m (21650ft).
The Bf.109G-14 arrived in July 1944 at the frontlines in France. It was an attempt on creating a standard type which incorporated many changes introduced during production period of the G-6 which ended leading to many variants and a very decentralized production. The standarization was a failure, but, overall it offered improved combat performance as the MW.50 power boosting water injection (which increased power output to 1800ps (1775hp) and the Erla haube was now the standard canopy. Maximum speed was of 568 km/h (353mph) at sea level and 665 km/h (413mph) at 5000m (16400ft). A high-altittude fighter, labelled as Bf.109G-14/AS was also produced with the DB605ASM engine as standard. That engine was now built with larger capacity supercharger and had higher rated altittude making the top speed of this variant to 560 km/h (348mph) at sea level and 680km/h (422mph) at 7500m (24600ft) high.
The tendency was to use plywood in some non-vital parts of the aircraft like the taller tailfin/rudder unit, pilot seat or instrument panel. Approximately 5500 Bf.109G-14 and G-14/AS were built.

Sources:
1. https://en.wikipedia.org/wiki/Messerschmitt_Bf_109_variants#Bf_109G
2. Salamander Books - The Complete Book of Fighters