despite the numerical designations the P-46 and P-60 were much earlier in timing than the P-40Q,
So early that their impact on the P-40Q project was just about nonexistent. (my opinion)
The Army ordered two XP-46s in Sept of 1939. They were to use the newly announced (but not anywhere production) V-1710-39. the Stripped prototype (no guns, armor, self sealing tanks, etc) flew in Feb 1941, the fully equipped version flew in Sept 1941 but it was an academic exercise. It had been decided in 1940 to build the P-40D using the same engine and without a miracle (fully equipped P-46 does well over 400mph?) the XP-46 was a dead duck in late 1940 to mid 1941. The P-40D entered production in May of 1941. The Prototype P-40F flew June 30th 1941.
The XP-60 started as the XP-53 (from Joe Baugher's web site)
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This was the Curtiss Model 88, which was basically an improved XP-46 powered by the yet-to-be-built 1600-hp Continental XIV-1430-3 twelve-cylinder liquid-cooled inverted Vee engine. The Model 88 was to use the fuselage and tail assembly of the P-40D combined with a NACA laminar flow wing."
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On October 1, 1940, the USAAC ordered two examples of the Model 88 under the designation XP-53"
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However, in a conference held six weeks later, the USAAC informed Curtiss-Wright of its need for a fighter combining laminar flow wing technology with the British Rolls-Royce Merlin engine. Since the XP-53 was already being designed for laminar-flow wings, Curtiss proposed to convert the second XP-53 airframe (41-19508) to the Merlin engine while it was undergoing construction"
"The Model 90 (XP-60) flew for the first time on September 18, 1941, only eleven days before the first flight of the disappointing XP-46. The performance of the XP-60 was disappointing as well, with a top speed of only 387 mph at 22,000 feet."
Yes the XP-60 project staggered on for while but it was just desperate attempts to find a powerful enough engine for an oversized and overweight airframe.
" However, on November 17, 1941, it was concluded that the P-60A would be underpowered if the Allison engine were used, and that either a more powerful engine should be found or else another fighter be built instead of the P-60A"
So three weeks before Pearl Harbor the 3rd version of the P-53/60 is considered to be underpowered with a turbocharged Allison of a proposed 1425hp model.
The P-40Q was nearly 2 years later. Two P-40Ks were modified and one P-40N. Several different 2 stage Allisons were used (one airframe got two, if not three, different engines) and while fast there seems to be a disconnect between the weight/armament of the prototypes and the intended service armament. The first pilot's report on
http://www.wwiiaircraftperformance.org
says that they were flying the plane at 8200lb with 160 gallons but armament is not listed, This was in Nov 1943.
By April of 1944 (how many Mustangs being built per month by then?) using a different engine the weight is given as 9000lbs with full fuel (unspecified but 150-160 gallons?) full oil, 11 gallons of water for the injection system but only four .50 cal guns with 235rpg. Production armament was suggested to be either six .50 cal guns or four 20mm cannon.
Six guns with 275 rpg would add around 360lb or more to the weight.
I don't know when Allison was promising what with the 2 stage supercharger but in 1942 and very early 1943 they were fooling around with a prototype engine that used the same size impeller in the auxiliary supercharger as the main supercharger, direct mechanical (single speed-drive) and a few other features that would not see the light of day on a production engine. Until Allison could come up with at least a viable prototype 2 stage engine the P-40Q project was going nowhere and having the Curtiss engineers and prototype shop workmen sit on their hands for several years by canceling the XP-46 and P-60 projects was not going to speed up the P-40Q/
The first V-1710-101 as used in the early P-40Q was not tested on a ground stand until July of 1943.