Martlet Mk II - 472 km/h (293 mph) at 2,962m and 3965m. Range 1432 km (889 miles) [Four gun, two speed Twin Wasp engine, some had 'retro-fitted' folding wings. On Formidable and Illustrious]
Martlet Mk III - 502 km/h (311 mph) at 4,877m. Range 1328 km (825 miles) [aka Wildcat Mk III, two speed R-1830-90 Twin Wasp. Originally Greek order, went to 805 and 806 Sqn]
This is where things get messy
After the Martlet I from the French contract, Britain took up the option clause therein for another 100 aircraft which were to be delivered as Martlet II. The first 10 were delivered in March 1941 arriving in the UK in June. Then Britain decided it would rather have the folding wing version, so delivery of the remaining 90 aircraft was delayed to take advantage of this. Deliveries of these 90 with folding wings began in late 1941, the first arriving in the UK in Dec 1941 with them forming the core of the Martlet II squadrons on Illustrious & Formidable in the IO in early 1942.
So the initial 10 fixed wing aircraft were redesigated Martlet III (along with 30 from the Greek contract that went straight to the Middle East)
There are reports that the original 10 Martlet III were retrofitted with folding wings but no evidence to back that up, except for a single fixed wing Martlet (serial unknown AFAIK) where the conversion was reported as being carried out by maintenance personnel on Illustrious as she sailed south to Cape Town after it had been damaged in a flight deck accident.