Despite the small numbers, they apparently made a mark on the minds of at least some allies and opponents. From wiki about the Macchi:
"Group Captain Duncan-Smith DSO DFC respected both the Macchi 'Veltro' and the Italian airmen: In general the standard of flying of the Italian pilots was very high indeed, and in encounters with Macchi 205s particularly we were up against aircraft that could turn and dog-fight with our Spitfires extremely well.[14] Like its predecessors, the first Veltros were insufficiently armed, but the aircraft often performed well in combat. Guido Carestiato said about the C.205, that it was the "best Italian fighter that he knew" and many pilots like the C.205 "ace" Luigi Gorrini,[15] scored 19 or 24 victories (in return, he was downed four or five times). Gorrini claimed 12 victories in July 1943 and several of them were with the Veltro.[16]"
Wiki regarding the Fiat G.55:
"In February 1943, a German test commission was sent in Italy to evaluate the new Italian fighters.[16] The commission was led by Oberst Petersen and was formed by Luftwaffe officers and pilots and by technical personnel, among them the Flugbaumeister Malz. The Germans also brought with them several aircraft including a Fw 190 A-5 and a Bf 109 G-4 for direct comparison tests in simulated dogfights.
The tests began 20 February 1943 with the German commission very impressed by the Italian aircraft, the G.55 in particular. In general, all the Serie 5 fighters were very good at low altitudes, but the G.55 was also competitive with its German opponents in term of speed and climb rate at high altitudes still maintaining superior handling characteristics. The definitive evaluation by the German commission was "excellent" for the G.55, "excellent" for the Re.2005 but very complicated to produce and "average" for the C.205. Oberst Petersen defined the G.55 "the best fighter in the Axis" and immediately telegraphed his impressions to Goering. After listening the recommendations of Petersen, Milch and Galland, a meeting held by Goering on 22 February 1943 voted to produce the G.55 in Germany."
also:
"The interest in the G.55 program was still high after the Armistice. In October 1943, Kurt Tank, who previously personally tested a G.55 in Rechlin, having nothing but praise for the aircraft, was in Turin to discuss G.55 production. However, war events and the not yet optimized production process were the reasons for which the G.55 program was eventually abandoned by the Luftwaffe. Early production of G.55 required about 15,000 man-hours; while there were estimations to reduce the effort to about 9,000 man-hours, the German factories were able to assemble a Bf 109 in only 5,000 man-hours. The DB 603 were instead to be used in Tank's own Ta-152 C."
Well armed, fast and reputedly maneuverable, as good as they were, they were evidently hard to assemble and slow to service (fuel and rearm).
The Fiat was armed with there 20mm (1 in each wing and 1 in the engine) and two fuselage mounted 12.7 mm. It had a WEP max speed of 417 mph at 23,000 ft.